The improvised explosive device in a white bucket blew up on the final carriage of the Parsons Green train credit: Pricey1983aa/Twitter

The army will deploy troops at key locations around the capital in order to free up police who were last night involved in a huge manhunt to catch the terrorist responsible for the failed Parsons Green bomb attack, which Islamic State of Iraq and the Levant claimed responsibility.

At least 29 people were injured, including a boy believed to be aged about 10 when an improvised explosive device (IED) went off on a packed rush hour tube at Parsons Green in west London yesterday morning.

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Witnesses described scenes of terror and panic after the blast sent a "fireball" and a "wall of flame" through a District line service in west London.

But the main device, which had been fitted with a crude timer using shop-bought fairy lights, failed to detonate, meaning hundreds of people were spared death and serious injury.

An injured woman is assisted by a police officer close to Parsons Green station credit: Stefan Rousseau/PA

Anti-terror police are understood to be working on the theory that the bomb was detonated early by accident and that the intended target may have been the Tube station at Westminster.

The attack - the fifth terrorist attack on the UK in just six months - caused a diplomatic row between Washington and London.

Donald Trump seemed to accuse the Metropolitan Police of knowing the identity of the attacker in advance but failing to prevent the bombing. Mr Trump posted on Twitter: “Another attack in London by a loser terrorist. These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”

His claim earned the US President a stiff rebuke from Theresa May. “I never think it’s helpful for anybody to speculate on what is an ongoing investigation,” said the prime minister. “The police and security services are working to discover the full circumstances of this cowardly attack and to identify all those responsible.”

Despite Mr Trump’s suggestion that the terrorist was known to police, counter-terrorism sources insisted that was not the case and that the hunt for the perpetrator of the bombing on a District Line train was ongoing.

Forensic officers work at the Parsons Green Underground Station after the blast credit: PA

Counter terrorism specialists from Scotland Yard were last night working to establish his identity from CCTV footage on the train and at stations on the line. They were also combing through records of payments with Oyster cards used to buy Tube tickets.

One theory is the suspected bomber may have fled the scene among the stampede of panicking passengers and escaped among the crowds.

They were also uncertain that Parsons Green was not the planned target, pointing to reports that the bomb, which was packed with shrapnel and contained a timing device, had apparently malfunctioned.

Watch live: Scene outside Parsons Green station

Witnesses reported seeing people "covered in blood" after a "flash and a bang" from the device, but sent a "fireball" through the packed Tube train.

Pictures and video posted on social media showed a flaming bucket - which appeared to have wires coming from it - inside a Lidl carrier bag on the floor of a carriage.

The device is not believed to have fully detonated and it is reported that it could have been set off on a timer.

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More follows - stay with us for the latest updates through the day

11:14PM Tightened security ahead of Chelsea v Arsenal game

In a statement, Chelsea said: "Following Friday morning’s incident at Parsons Green, and in order to help us fully prepare for the game, the majority of the Stamford Bridge site will remain closed until Sunday morning.

"This includes Stadium Tours, the Museum, Megastore and the Chelsea Health Club & Spa, while the ticket office will be operating via telephone and online only.

"During that time, entrance to the site will be via the Stamford Gate entrance only. On Sunday, we urge supporters to arrive at least one hour before kick-off to allow for extra security measures.

"We also request that supporters do not bring bags as this will delay your entry to the stadium. The club continues to monitor events and liaise with the police and relevant authorities on supporter safety."

10:47PM Trump under fire in US over London bombing comments

Ben Cardin, a Democratic member of the Senate Intelligence Committee, backed Theresa May in her rebuke of Donald Trump over the London bombing David Millward reports.

“I think the Prime Minister of the UK was appropriate in calling the president out.”

John Cohen, former US counterterrorism official and now a professor at Rutgers University, also believed Mr Trump’s intervention was unhelpful.

“At this stage investigators are going to be doing everything they can to locate those involved in the attack, and in particular the bomb maker,” he told the New York Times.

“These types of statements — at this stage of the investigation — can undermine law enforcement efforts because it discloses key information that the investigators may be using to locate the attackers, and it could put peoples’ lives at risk.”

10:35PM Bomb 'highly likely' to be TATP - CNN

A source briefed by investigators told CNN that an initial assessment of the device indicates it is "highly likely" to have contained the explosive TATP but that this has not been confirmed. It also appeared to have been crude and poorly designed, the source said.

09:18PM 'Excellent progress' made in hunt for terrorist, police say

Met Assistant Commissioner, Mark Rowley, said the police were making "excellent progress" in the hunt for the terrorist.

He said officers were trawling through hundreds of hours of CCTV footage and 77 images and videos taken by members of the public at the scene were also being examined.

Mr Rowley said the IED had now been made safe and was being examined by specialist forensic scientists.

08:27PM Threat level raised to 'critical'

The UK's terror threat level has been raised from severe to critical, indicating a further attack may be imminent, following the Parsons Green Tube bomb, Prime Minister Theresa May said.

Army troops will be assisting the police with their duties, freeing up officers to continue their investigation into the attack.

08:04PM Islamic State claims responsibility for the attack

The Islamic State terror group has claimed responsibility for the attack, according to the Amaq news agency which has links to the group.

08:00PM White House defends Trump's comments on Parsons Green attack

Mr McMaster was asked about Donald Trump's comments this morning, in which he said the suspect of the bombing was "in the sights" of Scotland Yard.

Theresa May called that speculation "unhelpful".

National security adviser H.R. McMaster, right, and U.S. Ambassador to the UN Nikki Haley, participate in a news briefing at the White House, in Washington credit: Carolyn Kaster

Mr McMaster said he thought the president was speaking in general terms, and did not have any specific information.

He said: "I think what the president was communicating was that all our law enforcement efforts are focused on this threat for years.

"Scotland Yard is a leader in this, and if it happened here in the US the FBI would also have the suspect in their sights.

"I think he means generally this kind of activity is what we are trying to prevent."

06:29PM President Trump calls for renewed effort to cut terror funding

H.R. McMaster, Donald Trump's national security adviser, has just spoken about the Parsons Green attack in the White House, Harriet Alexander reports.

He said: "The US stands in solidarity with the people of the UK.

"We will defend our people and our values against these cowardly attacks, and we will always stand by countries who do the same."

He said Mr Trump had been "unambiguous" in his policy on terrorism, urging a renewed effort at cutting financing for terrorist networks.

05:57PM President Trump speaks to PM to express sympathy

The White House press secretary has revealed details of the phone call between Donald Trump and Theresa May. The US president phoned to "convey his sympathies and prayers for those injured in the terrorist attack today in London", the White House said.

"The President pledged to continue close collaboration with the United Kingdom to stop attacks worldwide targeting innocent civilians and to combat extremism. "

A Downing Street spokesman said: "President Trump called the Prime Minister earlier today to offer his condolences over this morning's cowardly attack in London.

"They also discussed North Korea's latest missile test, agreeing it was a reckless provocation and that China must now use all its leverage to bring pressure to bear on the North Korean regime to ensure they change course and end these illegal tests."

05:49PM Number of injured rises to 29

NHS England says 29 people have been treated after the explosion at Parsons Green tube station.

As of 5.30pm on Friday, NHS England said it was now treating 21 patients.

Eight others were discharged earlier in the day.

05:35PM How will CCTV help track down suspect?

The installation of CCTV cameras on the London Underground network could play a key role in finding the perpetrator of the Parsons Green explosion.

S7 trains such as the one involved in Friday's incident have video cameras installed inside all seven carriages.

There are a total of more than 12,000 cameras across London Underground's stations and trains.

The footage is managed and recorded locally, although British Transport Police say they can also view much of it at their hub to "develop intelligence about particular locations and suspects".

CCTV can allow them to "identify and follow suspects" and provide "powerful evidence in court", according to the force.

Detectives could scour footage from the tens of thousands of cameras across London as a whole in a bid to trace whoever is behind the blast.

05:14PM 'Police need more resources to boost safety' - security experts

British Transport Police (BTP) should be given more resources to boost safety on London Underground, a security expert has said.

Deploying more officers should be prioritised over installing check points at Tube stations, according to Will Geddes, founder of private security firm International Corporate Protection.

Introducing airport-style barriers "is not necessarily going to be a solution" because of the huge number of passengers using the network.

"The terrorist is always going to look for the path of least resistance," he said.

"If you've got additional checkpoints on the exterior of the airport or the Tube station, you create a choke point, you create a build-up of individuals which could be exploited.

"What will hopefully happen is BTP will be given more resources to continue initiatives they're currently running, where they have periodic sweeps by plain-clothed covert officers who are carrying out hostile surveillance detection.

"They're ideally picking up on individuals who might be planning to do something or are in the right position to be able to react as quickly as possible should something happen."

Around 700 uniformed BTP personnel are deployed on the Tube and Docklands Light Railway, part of 3,000 across the capital's transport network.

Mr Geddes said passengers play a "critical part" in combating terrorism.

"It couldn't be more true, especially on the Underground," he said.

"You've seen the posters, you've heard the announcements. If you see an unattended package, or something else suspicious, report it.

"It's really, really key. The general public are the eyes and ears on the ground."

A bomb blast tore through an underground train deep in St Petersburg, Russia, on April 3, killing 11 people.

About 100 people were killed when two bombs were detonated outside Ankara train station in Turkey in October 2015.

03:46PM Locals offer tea and pizza to those caught up in attack

Free pizza, cups of tea and spare phone chargers were on offer around Parsons Green as well-meaning residents sprung into action following the outrage.

West Londoners fastened signs to their front doors telling anyone affected to come if they need anything from a beverage to a toilet break.

A note pinned outside two houses close to Parsons Green station welcoming strangers inside credit: Tess De La Mare /PA

At the fringes of the police cordon, Teo Citino, the owner of nearby restaurant Il Pagliaccio, piled a fold-out table with free pizza for the emergency services.

The 52-year-old said: "One of the reasons I'm here is that my wife and daughter could have been on that train, I live next to the station. I rang my wife right away, they were evacuated from the house in pyjamas.

"I must admit, I have been very, very lucky because they usually get the train to go to my daughter's school, she is 12 years old.

"My second reason is that it is a way to say thank you to those who provide services - the fire brigade, police and nurses - because I don't believe they receive enough money."

Staff from a local Italian restaurant hand out pizza and water from a stall near Parsons Green station credit: HANNAH MCKAY/Reuters

Other residents from near the site of the attack approached members of the Press and offered them access to phone chargers and a place to sit down inside.

Hammersmith and Fulham Council was also on hand, opening a local community centre as a rest place for those whose homes were within the police cordon.

Social media was similarly awash with people offering a comforting hot drink to those caught up in the aftermath.

03:39PM Bucket bomb seen before in failed UK terror attacks

The improvised bucket bomb left on the Tube at Parsons Green bears the hallmarks of previous failed bombing attempts in the UK, according to experts.

Academics and chemical experts suggested that, while the device caused what witnesses described as a "fireball", it failed to fully detonate.

Dr Lewis Herrington, a lecturer and terrorism expert at Loughborough University, said the use of a timer was "key", as it distinguished it from the suicide attacks on July 7 2005 and at the Manchester Arena earlier this year.

He said: "A timing device is critical - if you look at all the other attacks, the Westminster attack, Khuram Butt, Salman Abedi, they all wanted to die.

"That's not present and that really sends alarm bells. This guy really wanted to pack a punch.

"The initiator succeeded hence the reported fireball but clearly the explosive element failed."

Passengers react to the bomb attack at Parsons Green Tube station credit: HANNAH MCKAY/Reuters

Dr Herrington said the attack instead bore echoes of the case of Damon Smith, 20, who was jailed for 15 years in May after leaving a home-made bomb in a rucksack containing ball bearing shrapnel on a Jubilee Line train.

Smith, who had autism and was not motivated by terrorism, created the bomb after finding a guide online.

03:19PM Area around Parsons Green evacuated so 'remnants of bomb' can be secured

Scotland Yard said the area surrounding Parsons Green Tube station has been evacuated so specialist officers could "secure the remnants of the improvised device and ensure it is stable".

A spokesman added: "A small number of residents will be affected by the evacuation, which encompasses an area approximately 50 metres in radius." The Tube station remains closed.

Forensics officers, one is a gas mask, next to the evacuated Tube train credit: Peter Macdiarmid/LNP

Meanwhile, more than 50 residents evacuated following the attack are being looked after at the Lancaster Court community centre, reports Nicola Harley.

Council officers said they do not know how long people will be stuck here.

An armed police officer moves through pedestrians at Parsons Green credit: DANIEL LEAL-OLIVAS/AFP

03:13PM Donald Trump: 'We have to be very, very tough'

Asked about the London terror attack by reporters outside the White House in Washington, US President Donald Trump said: "It's a terrible thing. It just keeps going and going, and we have to be very smart, we have to be very, very tough. Perhaps we are not nearly tough enough.

"It's just an absolutely terrible thing. In fact, I'm going to call the Prime Minister right now. We have to be tougher and we have to be smarter."

03:11PM Security services have 'identified suspect from CCTV' - report

The security services have identified a suspect in the Parsons Green bombing from CCTV footage, according to an unconfirmed report by Sky News.

03:02PM Tube commuter: I thought I was going to die

Passenger Emma Stevie was in the Tube carriage when the device exploded. Here she describes the moment people were crushed as they tried to escape:

02:52PM Theresa May condemns 'cowardly' attack - and rebukes Donald Trump over tweet

Theresa May has rebuked US President Donald Trump over his Parsons Green comments on Twitter, saying: "I never think it's helpful for anybody to speculate on what is an ongoing investigation."

The Prime Minister also condemned the "cowardly" attack, saying: "This was a device intended to cause significant harm."

She also confirmed that the UK terror threat level remains unchanged at severe and is not being raised to critical.

Mrs May was speaking following a meeting of the Government's emergency Cobra committee.

02:47PM Scotland Yard: Donald Trump's Tube bomber comments 'unhelpful and pure speculation'

Scotland Yard has dismissed a claim by Donald Trump that the Parsons Green Tube bombers had been "in the sights" of police as "pure speculation".

A spokesman for the Metropolitan Police said the US president's comments - which did not correspond with any information released by the UK authorities - were "unhelpful".

Mr Trump made the provocative allegation in a trademark tweet as police launched a major manhunt to track down the perpetrators responsible for planting the device on a packed commuter train.

"Another attack in London by a loser terrorist," he wrote. "These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!"

His claim threatened to spark a fresh row over US-UK intelligence sharing arrangements which have already come under strain since he entered the White House.

A Scotland Yard spokesman said: "The comments are unhelpful and pure speculation. If anyone has got any evidence or information, please contact the anti-terrorism hotline."

02:39PM 'They were shouting 'stop, stop, stop'': Passenger describes crush chaos

Tube passenger Ryan Barnett said there was a crush of people on the stairs as commuters ran from the scene of the blast.

The 25-year-old, who works in politics and had been travelling to his office, said: "The stewards and other passengers, they are shouting 'stop, stop, stop', so I ended up squashed on the staircase, people were falling over, people fainting, crying, there were little kids clinging on to the back of me.

"It is absolute chaos, it was quite scary because at one stage we thought we might be trapped there - I heard a pregnant woman lost her shoes and had fallen over."

A police officer next to the carriage from which passengers fled on Friday morning credit: AP

02:20PM Police forensics officers scour carriage where bomb was detonated

Here are the latest pictures reaching us from Parsons Green as police forensics officers continue to examine the device that partially exploded and the Tube train.

Meanwhile, other detectives are scouring CCTV footage and examining witness statements for potential leads.

Forensic investigators search on the platform at Parsons Green Tube station on Friday afternoon credit: HANNAH MCKAY /REUTERS

Forensics officers next to the evacuated Tube train at Parsons Green credit: Peter Macdiarmid/LNP

The affected carriage was the final one of the District Line train credit: Frank Augstein/AP

01:50PM Parsons Green bomb comes after four UK terror attacks so far this year

The blast comes with the UK on high alert following four terrorist attacks so far this year.

Authorities have foiled 19 plots since the middle of 2013 - including six since the Westminster atrocity in March.

The incident comes a day after figures revealed terror-related arrests in Britain have hit a new record high, with suspects held at a rate of more than one every day.

Police and MI5 are running 500 investigations involving 3,000 individuals at any one time, while there are also 20,000 former "subjects of interest" whose risk must be kept under review

Here's a reminder of the UK terror attacks since 2005:

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01:33PM 'There was a stampede and people started crushing each other'

Standing outside St Thomas and Guy's Hospital, a woman who was on the Tube when the blast happened, told The Telegraph's Harry Yorke: "I was stood at the opposite end of the Tube, in the front carriage. I was on my way to work.

"I didn't hear anything, we just heard people screaming. We just ran to the exit, but there was a stampede and people started crushing each other.

"People were just scrambling and trying to get out through the entrance. My sister was in the carriage and was injured in the blast."

The woman, who wished to remain anonymous, said her sister had been taken to A&E and was currently being treated for burns.

01:28PM Commuter in blast carriage tells of 'flaming orange' fireball

Tube passenger Lauren Hubbard, who was end in the end carriage of the train with her boyfriend, said she heard a loud bang and saw a "fireball" coming towards her, reports Laura Hughes.

Lauren Hubbard, 24, who was in the end carriage of the train with her boyfriend, said she heard a loud bang and saw a "fire ball" coming towards her.

She told the Telegraph: "It was hot and just came towards you, this flaming orange coming towards you. It smelt like burning.

"We ran and hid behind cement boxes on the tracks and were the last people to get off the platform."

She added that her first thought was: "This is a terrorist attack, I'm going to die."

Another witness, who works next to the station, said he saw people pouring out the station looking "shellshocked" and "panicked".

Emergency services tend to an injured woman following the blast credit: GUSTAVO VIEIRA/Reuters

A woman with blankets wrapped around her is escorted by emergency services credit: Sky/AP

Injured passengers are led away from the scene credit: LUKE MACGREGOR/Reuters

Another witness told the BBC: "I was walking towards the station and suddenly lots of people came running down the stairs shocked and tearful and saying that there had been an explosion.

"People were saying there had been a wall of flames coming down the Tube carriage. I turned around and came back from the Tube station with all of them."

01:15PM Police confirm no arrests so far as manhunt continues

Scotland Yard have confirmed that no arrests have so far been made.

A spokesman said: "Detectives from the Counter Terrorism Command, part of the national counter-terrorism police network, are making fast-time inquiries to establish who was responsible and are working closely with the security services. So far there have been no arrests."

01:06PM The passengers who fled along train tracks after blast

Passenger Jose Sarango was on a Tube train about to pull into Parsons Green as terrified commuters began along the tracks opposite to flee the device, reports Steve Bird.

“We had nearly reached Parsons Green at about 8.25am when our train from Victoria suddenly stopped. The driver announced that there was a problem with the train ahead.

“That was when we saw people, mainly adults and many wearing suits, filing nervously along the train tracks opposite away from the station towards Fulham.

"Many of them looked panicked as they tried to pass trains stacked up. Some of them were running and looking behind at the train they had just been on in the station. They were clearly very worried.”

Emergency workers help people leave a Tube train near Parsons Green credit: AP

Mr Sarango, a 52-year-old cleaner from Stockwell who was travelling to Parsons Green to have breakfast with his wife before work, said he was stuck on his train for an hour and watched as scores of passengers fled past his carriage.

“The driver then told the passengers to move to the back and we were let off to walk along the tracks,” he continued.

“I felt very nervous. No one knew exactly what was happening. People had begun looking at their phones and saw reports of people saying there had been some kind of explosion. That news meant we were even more worried.”

Passengers are led away from a District Line Tube at Parsons Green credit: AP

Mr Sarango and his fellow passengers were led down a back route along the tracks to Parsons Green.

“I was reassured to see lots of armed police, police cars and sniffer dogs. But, it was scarey.”

His wife, Cecelia Velez, had been waiting to have breakfast at Gail’s coffee shop on Fulham Road before their shift as cleaners at a local shop.

When she called him he warned her about the terror fears. Minutes later, police ordered her and staff at the restaurant to take cover downstairs.

“I suffer a blood pressure condition. And, I could feel my blood pressure drop,” she said. “We didn’t know what was going on, we were simply told that there had been an ‘incident’, but our phones told us otherwise.

“I still feel a little cold, but the staff here have given me coffee and sugar to help.”

12:42PM Amber Rudd condemns 'callous and indiscriminate' attack

Home Secretary Amber Rudd has condemned the Parsons Green blast, saying: "Once more people going about their everyday lives have been targeted in a callous and indiscriminate way.

"My thoughts are with all those injured and affected. The police and emergency services were quickly on the scene and I would like to pay tribute again to their professionalism and tireless commitment.

"I am receiving regular updates on what is an ongoing and active investigation. I would urge Londoners to remain alert and assist the police and emergency services as much as they can."

12:35PM Sadiq Khan: An attempt by evil and cowardly... to disrupt our way of life

The mayor of London, Sadiq Khan, has issued a statement in which he said: "This was an attempt by evil and cowardly individuals to kill and disrupt our way of life."

Mr Khan told LBC: "There is a manhunt under way as we speak."

Sadiq Khan: Blast shows threat facing London

12:34PM Residents evacuated as police check for any other potential devices

Residents surrounding the Tube station have been evacuated from homes as police check for any other potential devices, reports Nicola Harley.

"There are searching homes, workmen told me they are checking for any other devices," a witness said. "We don't know when they will let us return."

Armed police officers walk through the carriage of a London underground tube carriage at Parsons Green credit: DANIEL LEAL-OLIVAS/AFP

Witness Luke Warmsley was in the carriage where the device exploded.

"It was like a large match had gone off at the end of the carriage," he told LBC radio.

"There was a plume of smoke that went off. I looked down the carriage and just saw more and more people running towards me."

Police cordon off an area of Parsons Green credit: JEFF GILBERT for The Telegraph

Another witness said she saw people with burns and medics were placing plastic over their injuries.

12:27PM Council leader 'outraged' by explosion

Stephen Cowan, the leader of Hammersmith and Fulham Council, the area in which the attack took place, said he was "outraged" by the explosion. He said:

"Around 8.20 this morning a package exploded in the final carriage of a District Line train at Parsons Green station, it is being treated as a terrorist incident. "What is extremely impressive was that the emergency services were on to the situation immediately, there is a completely co-ordinated effort and there is no reason to be overly concerned. "I would stress that people should be reassured because this is being dealt with very effectively by everyone in the emergency services. "I can't tell you how angry I am, I am absolutely outraged that someone could do this - attacking innocent lives, putting those people at risk and causing fear and harm is not a way to express yourself. "This kind of terrorism needs to be stamped out, but people need to recognise that in London we have one of the most amazing cities anywhere, they are not going to damage us, they are not going to beat us."

12:20PM Total number of those injured in Parsons Green rises to 22

In addition to the 18 victims taken to hospital by ambulance, four others took themselves to hospital, the NHS said. Here is where they are being treated:

Imperial - three patients

Chelsea and Westminster - eight

Guy’s and St Thomas’ - eight

Central London Community Healthcare Urgent Care Centre in Parsons Green - three

An injured woman is assisted by a police officer close to Parsons Green station credit: Dominic Lipinski/PA

12:09PM Jeremy Corbyn thanks emergency services for response

Writing on Twitter, Labour leader Jeremy Corbyn has thanked the emergency services for their response to the terror attack:

11:50AM Donald Trump denounces attack by 'loser terrorist'

US President Donald Trump has denounced the attack by a "loser terrorist", suggesting that such attackers "were in the sights of Scotland Yard":

11:43AM Police: Blast caused by 'detonation of improvised explosive device'

Assistant Commissioner Mark Rowley said the Parsons Green explosion was caused by the "detonation of an improvised explosive device".

Mr Rowley said it was understood that "most" of the 18 injured were suffering from "flash burns".

He added that:

Hundreds of detectives are involved in the investigation - including scouring CCTV footage and speaking to witnesses

MI5 is supporting the police investigation

Londoners can expect to see an enhanced police presence on the capital's transport network this weekend

11:34AM Commuters tell of 'mass pile-up' trying to flee Tube train

One witness told The Telegraph's Laura Hughes: "It was extraordinary - just panic as everyone legged it off the train.

"I got stuck in a mass pile-up as everyone tried to get down the stairs. People were falling on top of each other trying to get out."

Forensic investigators search next to a Tube train at Parsons Green credit: HANNAH MCKAY/REUTERS

A passenger on the train ahead, who gave his name only as Mike, told the Telegraph: "We were taken off the train at Fulham Broadway. The driver reported a mayday call had been received from Parsons Green."

11:24AM How long has a terror attack been 'highly likely' in the UK?

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11:23AM Ambulance service: 18 taken to hospital - none seriously injured

Eighteen people were taken to hospital after the Parsons Green explosion, London Ambulance Service said, adding that none are thought to be in a serious or life-threatening condition.

Natasha Wills, Assistant Director of Operations at London Ambulance Service, said:

“We can confirm we have taken 18 patients to hospital following the incident at Parsons Green underground station. “We were called at 8.20am today, with the first ambulance crew arriving within five minutes. “We have sent a number of resources to the scene including ambulance crews, officers and our Hazardous Area Response Team. “We are working closely with our colleagues from the Metropolitan Police, British Transport Police and London Fire Brigade at the scene; ensuring patients receive the medical help they need as quickly as possible. “As we are very busy dealing with this incident, we would ask the public to only call us in a genuine emergency.”

11:16AM Man who had his head charred by blast: 'I thought the whole train would blow up'

A man injured in the explosion described the moment the fireball engulfed his train, charring his head.

Peter Crowley said: "Everyone ran off the Tube. It was panic stations - my initial thought was that the whole train would blow up.

"I saw passengers with facial burns, they had been exposed to a very, very hot fire for a nano second, it was lucky doors were open because everyone just got off the Tube.

"It was a terrifying experience, I am lucky I got away with just a bit of charred hair."

Click here to read more.

Peter Crowley had his head charred in the explosion credit: Peter Crowley/Twitter

10:52AM Sadiq Khan: London will never be intimidated or defeated by terrorism

Mayor of London Sadiq Khan has appealed for calm following the Parsons Green terror incident, saying London "will never be intimidated or defeated by terrorism".

10:51AM 'Device' was in a 'white builder's bucket' inside Lidl bag

Chris Wildish, who was on the train, said he saw a "device" in the last carriage.

"It was a white bucket, a builder's bucket," he told BBC 5 live.

"Flames were still coming out of it when I saw it and had a lot of wires hanging out of it - I can only assume it was done on purpose.

"It was standing against the door of the rear-most carriage."

Little damage appeared to have been caused to the carriage after the explosion in a white bucket credit: Sylvain Pennec/PA

10:45AM Major incident declared at St Mary's Hospital

A major incident has been declared at St Mary's Hospital in Paddington in response to the Parsons Green explosion.

Meanwhile, several ambulances have arrived at Chelsea and Westminster Hospital coming from the Parsons Green direction, reports Harry Yorke.

At the entrance of A&E there are a small team of paramedics gathered at the door awaiting further casualties.

Members of the emergency services work alongside an Underground tube train at a platform at Parsons Green credit: DANIEL LEAL-OLIVAS/AFP

A person from the first ambulance was carried into the hospital on a stretcher and cloaked in foil, using breathing apparatus, he said.

Two men have exited the second ambulance and are talking to paramedics outside of the A&E department. They are both cloaked in red shawls and are carrying two rucksacks.

10:42AM 'I heard a boom... then there were flames all around': Witness describes scene of panic

Sylvain Pennec, a software developer from Southfields, near Wimbledon, was around 30ft from the source of the explosion when fire filled the carriage.

"I heard a boom and when I looked there were flames all around," he said.

"People started to run but we were lucky to be stopping at Parsons Green as the door started to open."

Personal belonglongs and a bucket with an item on fire inside it on the floor of an underground train carriage at Parsons Green station credit: SYLVAIN PENNEC/REUTERS

Mr Pennec described the scene of panic as commuters struggled to escape the carriage, "collapsing and pushing" each other.

Mr Pennec stayed behind to take a closer look at what he believed was the source of the explosion.

"It looked like a bucket of mayonnaise," he said.

"I'm not sure if it was a chemical reaction or something else, but it looked home-made. I'm not an expert though."

10:32AM Theresa May: Thoughts are with those injured at Parsons Green

10:21AM Latest statement from Met Police confirms it is being treated as 'terrorist incident'

Scotland Yard has issued a new statement confirming the blast is being treated as a terrorist incident:

"Officers from the Met's Counter Terrorism Command are investigating after an incident on a London tube train this morning. "Police were called at approximately 08:20hrs on Friday, 15 September to Parsons Green Underground Station following reports of a fire on the train. "Deputy Assistant Commissioner Neil Basu, the senior national coordinator for CT policing, has declared it a terrorist incident. "Officers from the Metropolitan Police Service and British Transport Police attended the scene, along with colleagues from the London Fire Brigade and London Ambulance Service. "At present we are aware of a number of people who have suffered injuries. "It is too early to confirm the cause of the fire, which will be subject to the investigation that is now underway by the Met's Counter Terrorism Command. "The station remains cordoned off and we are advising people to avoid the area. "Anyone who has information that would assist detectives is urged to contact the hotline 0800 789 321; if it's an emergency always call 999. "Anyone with images from the scene is asked to upload them to www.ukpoliceimageappeal.co.uk "We urge the public to remain calm but alert and if you have any concerns, see or hear anything suspicious then contact police."

10:16AM Parsons Green blast being treated as 'terrorism'

A police source has told the Telegraph: "We are treating it as suspected terrorism. We have not ruled terrorism in or out.

"We don't who it is. "We don't know if it's an organisation or individual."

10:14AM Armed police outside Parsons Green station

As a cordon remains in place around Parsons Green station, these are the latest pictures reaching us of armed police outside.

Counter-terror police from Scotland Yard are said to be "monitoring events", but the investigation remains in the hands of the British Transport Police.

Armed police officers outside the evacuated Parsons Green station credit: DANIEL LEAL-OLIVAS/AFP

A firearms officer at the police cordon in west London credit: DANIEL LEAL-OLIVAS/AFP

Armed police outside Parsons Green station credit: KEVIN COOMBS/Reuters

Meanwhile, armed police have been pictured on the tracks at Parsons Green:

10:05AM BBC's Sophie Raworth saw woman with 'burns all over her body from top to toe'

Sophie Raworth, the BBC News presenter who was at the scene, said she saw a woman on a stretcher with burns to her face and legs.

"I spoke to a woman, Laura Bishop, who said she was standing there and all of a sudden heard a bang - and saw a wall of flames, flames in the carriage," she said.

"She saw people who had burns on their hair, burns on their head and the doors opened immediately."

Ms Raworth added: "I have just seen a woman who was just stretchered off here and clearly her legs are wrapped up and she has burns.

"She had burns to her face - she's conscious, she was taking oxygen and pain relief as well.

"She seemed to have burns all over her body from top to toe."

An injured woman outside Parsons Green station credit: KEVIN COOMBS/Reuters

Speaking on the Victoria Derbyshire show, she told how a witness told her there was a stampede and then "panic, just complete panic".

She added: "There are a lot of people here at Parsons Green looking very anxious and worried, trying to work out what has happened. Clearly just trying to get out of the station itself was pandemonium."

A police officer direct people away from Parsons Green Tube station credit: KEVIN COOMBS/Reuters

09:44AM Boris Johnson: Everybody should keep calm and go about their lives in a normal way

Foreign Secretary Boris Johnson appealed for calm.

He told Sky News: "I'm afraid my information is limited and it really is important not to speculate at the moment.

"Obviously, everybody should keep calm and go about their lives in a normal way, as normal as they possibly can.

"As far as I understand it, the British Transport Police and TfL are on it and they will be updating their websites as and when we have more information."

09:40AM 'His face was covered in blood - I've never seen anything like it'

Another witness, Sham, said he saw a man with blood all over his face.

"There were loads of people crying and shaking," he told 5 live. "There were a lot of people limping and covered in blood.

"One guy I saw, his face was covered in blood - I've never seen anything like it."

A woman is spoken to by police outside Parsons Green station credit: KEVIN COOMBS/Reuters

Commuter Robyn Frost was arriving at the station when she saw people trying to escape.

She told the BBC: "I walked into the station, there was blood on the floor and people running down the stairs screaming 'get out'.

"People were coming out of the station covered in blood."

She added: "People have been stretchered into ambulances now."

09:39AM 'Everyone was crying and screaming' - witness

Passenger James Jackson said: "I was going in to the station. Suddenly I saw everyone pouring out of the station.

"Everyone was crying and screaming. I saw a woman carried into the cafe with bandages around her legs. My housemate was on the platform and thought it was an electrical explosion. It was the rear carriage that went off.

"I slept in I should have been on that train. I went to a cafe and the police have evacuated us all."

09:35AM Video shows smouldering bucket in train carriage

09:27AM Update from Metropolitan Police: Avoid the area

A Metropolitan Police spokesman said: "Police were called at approximately 08:20hrs on Friday, 15 September to Parsons Green Underground Station following reports of an incident on a tube train.

"Officers from the Metropolitan Police Service and British Transport Police are in attendance along with the London Fire Brigade and London Ambulance Service.

"We would advise people to avoid the area."

Emergency services outside Parsons Green credit: ASolopovas/Reuters

09:18AM 'Panic as people rushed from train' after hearing 'explosion'

BBC correspondent Riz Lateef, who was at the station travelling to work, said there was "panic as people rushed from the train, hearing what appeared to be an explosion.

"People were left with cuts and grazes from trying to flee the scene. There was lots of panic."

09:17AM London Ambulance Service sends hazardous area response team to scene

Natasha Wills, of London Ambulance Service said: "We were called at 8.20am to reports of an incident at Parsons Green underground station.

"We have sent multiple resources to the scene including single responders in cars, ambulance crews, incident response officers and our hazardous area response team, with the first of our medics arriving in under five minutes.

"Our initial priority is to assess the level and nature of injuries. More information will follow when we have it."

09:14AM People trampled as they tried to escape packed carriage

Media technology consultant Richard Aylmer-Hall, 53, was sitting on the District Line train bound for central London when panic unfolded at around 8.20am.

He said he saw several people injured, having apparently been trampled as they tried to escape. He said:

"I was blissfully reading my paper and listening to a podcast and suddenly the whole world charged past me down the platform, down the Tube. "I was on the Tube, we had just stopped at Parsons Green, I was on my way up from Wimbledon towards Paddington and suddenly there was panic, lots of people shouting, screaming, lots of screaming. "There was a woman on the platform who said she had seen a bag, a flash and a bang, so obviously something had gone off. "It was an absolutely packed, rush-hour District Line train from Wimbledon to Edgware Road. "I saw crying women, there was lots of shouting and screaming, there was a bit of a crush on the stairs going down to the streets. "Some people got pushed over and trampled on, I saw two women being treated by ambulance crews. "Since then, every emergency vehicle in London has gone past me, fire engines, ambulances, every type of police vehicle."

Mr Aylmer-Hall added: "I don't think anyone was hurt by the actual device or whatever it was."

09:07AM Emergency services outside station as passengers urged to use alternative routes

British Transport Police said: "We're aware of an incident at Parsons Green station. Officers are at the scene. The station is closed."

Transport for London said it is "investigating an incident at Parsons Green" and urged customers travelling between Wimbledon and Earls Court to use alternative routes.

A London Ambulance Service spokesman said: "We are on scene alongside the Metropolitan Police at Parsons Green."

London Fire Brigade said they were called to the incident at 8.21am on Friday.

Emergency services outside Parsons Green station credit: Richard Aylmer-Hall/PA

Emergency services outside Parsons Green station credit: Richard Aylmer-Hall/PA

08:56AM Passengers report 'huge stampede' at Parsons Green

08:52AM Pictures show injured passengers treated at scene

08:48AM Statement from Metropolitan Police

A Metropolitan Police spokesman said: "We are aware of an incident at Parsons Green Tube station. Officers are in attendance. More info ASAP".

08:47AM Picture shows 'exploded bag' on train carriage

A picture posted on social media appeared to show a bag that "exploded".

A Twitter user said: "Fireball flew down carriage and we just jumped out open door."

Transport for London said: "We are investigating an incident at Parsons Green.

"Customers travelling between Wimbledon and Earl's Court are advised to use alternative routes."