A reported explosion at a train station sent commuters stampeding in panic, injuring several people on September 15, at the height of London’s morning rush hour, and police said they were investigating it as a terrorist attack.

Emergency services said they were responding to an "incident" in which people were injured at Parsons Green Underground station in west London. The station was closed, as well as an entire section of the District Line where it is located.

Live updates (in IST):

September 16

11.10 am: Detectives used CCTV images from the station and train to single out the suspect believed to have planted the homemade device, but were still working to identify the bomber.

Raising the terror status to its highest level, which means another attack is considered imminent, Prime Minister Theresa May said military personnel would replace armed police “on guard duties at certain protected sites which are not accessible to the public“.

2.30 am: Military personnel are set to guard key sites across Britain, replacing police officers, as the independent Joint Terrorism Analysis Centre raised the nation’s threat level to critical, meaning an attack is expected imminently. “This is a proportionate and sensible step that should provide extra reassurance and protection while the investigation progresses,” Prime Minister Theresa May said late on Friday, following the explosion of the improvised device on a busy rush hour tube that injured at least 29 people.

Assistant Commissioner of the Metropolitan Police Mark Rowley said there was little doubt that the device had been intended to cause great harm and injury. Hundreds of police officers were working on the case, with 45 witnesses interviewed and 77 images and videos sent to the force by members of the public. “I urge communities across the UK to be vigilant and report any suspicious behavior to the police immediately,” he said, adding that the country could expect more armed and unarmed police on the streets, particularly at crowded places, iconic sites, transport hubs and ports. Security would also be enhanced at upcoming events.

ISIS has taken responsibility for the attack, according to a communiqué translated by the Site Intelligence Group, claiming that several devices had been planted, and that more “devastating” attacks were to come.

September 15

7:35 pm: Prime Minister Theresa May says Britain’s official threat level from terrorism remains at “severe,” meaning an attack is highly likely, and has not been raised in the wake of the London subway bombing.

After chairing a meeting of the government’s emergency committee, May said the threat level was not being raised to “critical,” which would mean an attack is imminent.

She says that decision will be kept under review. The threat level was briefly raised to critical after the May 22 suicide bombing at Manchester Arena.

6:30 pm: German and French leaders say the bomb attack on a London subway train only strengthens their determination to increase international cooperation in fighting terrorism.

Chancellor Angela Merkel said after meeting with French Prime Minister Edouard Philippe in Berlin on Friday- “Our thoughts are of course with the wounded, our thoughts are with the British population.”

Mr. Philippe said the London bomb and an attempt early Friday by a knife-wielding assailant to attack a soldier at a Paris subway interchange “show how much we collectively, in France, Britain and also in Germany, face a major threat.”

5:50 pm: British police say no one has been arrested in connection with a bombing on a London subway train, but hundreds of detectives are at work trying to hunt down the perpetrator or perpetrators.

The Metropolitan Police force says police “are making fast—time inquiries to establish who was responsible and are working closely with the security services.”

5:20 pm: U.S. President Donald Trump blasted the “loser terrorists” behind the train attack in London.

“Another attack in London by a loser terrorist,” the US president tweeted.

“These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”

He then added: “Loser terrorists must be dealt with in a much tougher manner,” without giving details of what that meant.

“The internet is their main recruitment tool which we must cut off & use better!” he added.

4:30 pm: The Scotland Yard has confirmed the detonation of an improvised explosive device (IED) was responsible for the explosion on the district line tube train at Parsons Green station in South West London at around 8.20 this morning.

Assistant Commissioner Mark Rowley, addressing journalists said that 18 people had been taken to hospital, with many of the injuries appearing to be flash burns. He said that hundreds of police officers were now involved in the live investigation led by the Metropolitan Police’s Counter-terrorism Command and that the public could expect to see an enhanced police presence, particularly across London transport.

The source of the explosion appears to be contained in a white container within a supermarket carrier bag on the packed commuter tube train headed to central London.

While witnesses spoke of people being trampled underfoot in the panic to escape from the station, which can be exited by just one narrow stairwell, the ambulance service is yet to confirm if some of the injuries were a result of this stampede.

4:00 pm: 18 people have been hospitalised after London train attack. Neither of them are in critical condition nor have been admitted with life-threatening injuries, says London Ambulance Service, which ferried the injured to nearby hospitals.

3.25 pm: “Our city utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life,” says London Mayor Sadiq Khan. “As London has proven again and again we will never be intimidated or defeated by terrorism,” he added calling on Londoners to remain calm and vigilant.

3.10 pm: Our correspondent Vidya Ram reports:

It is the fifth terror attack in Britain since March, including the attack on Westminster Bridge and the Palace of Westminster, the attack on the Manchester Arena, the attack on London Bridge, and the attack outside the Finsbury Park Mosque in London. The current threat level for Britain is severe meaning an attack is highly likely. The Parsons Green attack has come twelve years after multiple attacks took place on London transport: buses and tube trains, killing 52 people.

Speaking at the incident, a Metropolitan Police spokesperson said they were investigating a “critical and extremely serious incident,” relating to what seemed like an “item exploding to a small degree.”

He said the state of the injuries as a result of the incident were still being assessed, though surrounding areas had been closed. “At this stage we are still in the very early stages and its too early to speculate on any next steps.”

One passenger who was on the carriage where the incident took place told the BBC he had heard a large bang and then a fireball above his head, which singed his hair. “A lot of people were worse off than me,” he said. Others spoke of panic as people attempted to leave the station.

3.00 pm: Police have confirmed that there was fire on London Tube train in which a number of people have been injured, according to AP.

Prime Minister Theresa May will chair a meeting of Britain's emergency response committee later on Friday, her office said in a statement, according to Reuters.

“My thoughts are with those injured at Parsons Green and the emergency services who, once again, are responding swiftly and bravely to a suspected terrorist incident,” May said in the statement.

The meeting of COBR, the emergency response committee, will take place at 1200 GMT.

2.50 pm: Metropolitan police have confirmed it is a terrorist incident, reports Vidya Ram from London. Counter terrorism command are investigating.

2.40 pm: London firefighters are leading passengers off a train along elevated subway tracks near where a reported explosion sent commuters fleeing in panic, reports AP. Video from the scene showed people picking their way along the tracks.

Police put up cordon tape nearby after an incident on a tube train police at Parsons Green subway station in London, Friday, Sept. 15, 2017. | Photo Credit: AP

Photos taken inside the District Line train show a white plastic bucket inside a supermarket shopping bag. Flames and what appear to be wires can be seen. Witnesses said commuters fled the station in a panic. London ambulance services said they had sent multiple crews to the scene, and police advised people to avoid the area.

2.30 pm: Reuters reports that British Prime Minister Theresa May is “receiving regular updates” on the "incident at tube station in west London". British counter-terrorism officers are now on the scene, the agency added.

British Foreign Secretary and former London mayor Boris Johnson appealed for calm. "I'm afraid my information is limited and it really is important not to speculate at the moment," AFP reports him speaking to Sky News.

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

2.20 pm: AFP reports quoting eyewitnesses:

Richard Aylmer-Hall, 52, a media technology consultant, described "panic" on the train. "There was panic, lots of people shouting, screaming, lots of screaming," he told the Press Association. "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," he said. "I saw two women being treated by ambulance crews," he said.

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."

Natasha Wills, assistant director of operations at London Ambulance Service said in a statement: "Our initial priority is to assess the level and nature of injuries". She said the ambulance service had sent "multiple resources" to the station, including a hazardous area response team.

2.15 pm: Vidya ram reports: Official sources tell BBC that counter-terror officers are on the scene too though we are yet to have confirmation of the nature of the attack.

2.10 pm: A commuter whose train had just left the Parsons Green station says there was panic after a woman on the platform saw what appeared to be an explosion. Richard Aylmer-Hall said he saw several people injured, apparently trampled as they fled. “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,” he said. “Some people got pushed over and trampled on, I saw two women being treated by ambulance crews.” He said he did not believe anyone was hurt by the actual device. The London ambulance service said multiple crews had been dispatched.

The incident happened during rush hour when the Underground system is crowded. Passengers were advised to use alternate routes.

AFP reports that a Twitter user @RRigs posted pictures of a white bucket smouldering on a train.

Explosion on Parsons Green district line train. Fireball flew down carriage and we just jumped out open door. pic.twitter.com/pGbfotbfsJ — Rigs (@RRigs) September 15, 2017

2.05 pm: Our London Correspondent Vidya Ram reports: Official sources are remaining cautious, about the “incident” on a train at around 8.20 a.m. local time at Parsons Green, a tube station in South West London. The Metropolitan Police said the would release facts when they could “our info must be accurate.” Armed police are on the scene with other emergency services.

London Ambulance Service has deployed a hazardous area response team and ambulance crews, with the first medics arriving within five minutes of the incident being reported. The Fire Brigade has around 50 firefighters and specialists officers on the scene after getting the call at 8.21 a.m. in the morning at the height of rush hour.

A photograph has emerged of a white container with a shopping bag on fire on a tube train. A reporter for the London daily tabloid Metro who was on the scene when the incident occurred spoke of seeing people with facial burns, while ambulances have begun to take injured passengers away from the scene.

2 pm: London Fire Brigade says six fire engines, two fire rescue units and around 50 firefighters and specialist officers are currently attending the “incident” at Parsons Green Tube station. The Brigade was called at 8.21 a.m. and fire crews from Fulham, Wandsworth, Chelsea, Hammersmith and other surrounding fire stations are in attendance, the Brigade said on its website.

An injured woman reacts outside Parsons Green tube station in London, Britain September 15, 2017. | Photo Credit: Reuters

1.55 pm: British Police advise people to avoid the area around Parsons Green after reports of explosion, Reuters reports. The Metropolitan Police tweeted that they were called at around 8.20 a.m. local time to Parsons Green following reports of an incident on a tube train.

1.45 pm: Transport for London said on Twitter that there was no service between Earls Court and Wimbledon on the District Line which runs through Parsons Green.

London Ambulance Service has sent hazardous area response team to Parsons Green, priority to assess level and nature of injuries, reports Reuters.

1.40 pm: Images posted on Twitter showed a woman being attended to by emergency services sitting on a pavement.

Police say they are aware of reports on social media and will release facts regarding the incident once they could be sure of their accuracy.

With inputs from agencies