What we know so far:

The Manchester Arena was hit by at least one explosion during a concert by Ariana Grande

Police confirm 22 Dead, around 59 injured

Police state it is 'possible terrorist incident'

UK officials suspect it was caused by suicide bomber.

Senior counter-terrorism officials meeting in London

Police warn people to stay away from area

Emergency services rush to scene

Ariana Grande 'Okay' following the incident

Here is the summary: A man armed with an “improvised” bomb has killed at least 22 people and injured 59 outside a concert arena filled with teenagers in central Manchester on Monday night, in the worst terrorism incident in the UK since 2005. Police said the bomber, who died in the explosion, detonated the device shortly after the end of a concert by US pop star Ariana Grande at about 10.30pm. The incident adds the northern English city to the growing list of recent western targets that includes London, Paris, Stockholm and Berlin.

Quoted by the FT, Ian Hopkins, chief constable of Greater Manchester police, said they were still attempting to determine whether the attacker “was acting alone or was part of a network”.

“This has been the most horrific incident we have had to face in Greater Manchester and one that we all hoped we would never see,” Mr Hopkins said at a news conference on Tuesday morning. “Families and many young people were out to enjoy a concert at the Manchester Arena and have lost their lives... We believe, at this stage, the attack last night was conducted by one man," Hopkins told reporters. "The priority is to establish whether he was acting alone or as part of a network.

British political leaders, who were in the middle of a general election race, halted all campaigning. Prime Minister Theresa May was scheduled to chair a meeting of the cabinet’s emergency Cobra committee on Tuesday morning.

“We are working to establish the full details of what is being treated by the police as an appalling terrorist attack,” Mrs May said. “All our thoughts are with the victims and the families of those who have been affected.”

Prime Minister Theresa May called an emergency meeting with intelligence chiefs on the deadliest militant assault in Britain since four British Muslims killed 52 people in suicide bombings on London's transport system in July 2005. Witnesses related the horror of the blast which prompted a stampede just as the concert ended at Europe's largest indoor arena.

"We ran and people were screaming around us and pushing on the stairs to go outside and people were falling down, girls were crying, and we saw these women being treated by paramedics having open wounds on their legs ... it was just chaos," said Sebastian Diaz, 19.



"It was literally just a minute after it ended, the lights came on and the bomb went off," Diaz said.



U.S. President Donald Trump described the attack as the work of "evil losers". German Chancellor Angela Merkel said it "will only strengthen our resolve to...work together with our British friends against those who plan and carry out such inhumane deeds."



According to AP, there was no immediate claim of responsibility. Online, supporters of the extremist Islamic State group, which holds territory in Iraq's Mosul and around its de facto capital in the Syrian city of Raqqa, celebrated the blast. One wrote: "May they taste what the weak people in Mosul and (Raqqa) experience from their being bombed and burned," according to the U.S.-based SITE Intelligence Group.

"A huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena," said concertgoer Majid Khan, 22. "It was one bang and essentially everyone from the other side of the arena where the bang was heard from suddenly came running towards us as they were trying to exit." Added Oliver Jones, 17: "The bang echoed around the foyer of the arena and people started to run." Video from inside the arena showed concertgoers screaming as they made their way out amid a sea of pink balloons.

British Prime Minister Theresa May said the government was working to establish "the full details of what is being treated by the police as an appalling terrorist attack." May is due to chair a meeting of the government's COBRA emergency committee later Tuesday. She and other candidates suspended campaigning for Britain's June 8 election after the blast.

Police advised the public to avoid the area around the Manchester Arena, and the train station near the arena, Victoria Station, was evacuated and all trains canceled.

The Dangerous Woman tour is the third concert tour by 23-year-old Grande and supports her third studio album, "Dangerous Woman." Grande's role as Cat Valentine on Nickelodeon's high school sitcom "Victorious" propelled her to teen idol status, starting in 2010.

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Update 14: No claim regaridng responsibility but several ISIS accounts celebrate the attack...

1) No claim regarding blast in #Manchester, but #ISIS accounts celebrating the attack, disseminating media & threats pic.twitter.com/Z8VqKWUkXD — Rita Katz (@Rita_Katz) May 23, 2017

Update 13 : Ariana Grande has tweeted she is "broken" following the suspected terrorist attack at Manchester Arena, adding: "From the bottom of my heart, I am so so sorry."...

broken.

from the bottom of my heart, i am so so sorry. i don't have words. — Ariana Grande (@ArianaGrande) May 23, 2017

Update 12: US Department Of Homeland Security has issued a statement:

@ABC @SadiqKhan MORE: DHS on #ManchesterArena incident: “No information to indicate a specific credible threat involving music venues" in the U.S. pic.twitter.com/6WABZRhk1m — ABC News Politics (@ABCPolitics) May 23, 2017

Update 11: The moment of the explosion - from within the arena...

Update 10: According to the Telegraph, the arena was packed with young children.

Jane Pearson, 46, a high school English language mentor from Chadderton, Greater Manchester, had gone to the concert with her daughter, Rachel, 21, as a birthday treat. She told PA the arena was packed full of young children. Mrs Pearson said: "It's the worst kind of people who could even consider doing something like this and quite frankly those sort of people, they deserve the worst punishment ever.

"I can't imagine what goes in to the heads of these people that want to hurt children? And families who have come together for such a happy occasion. It's disgusting. It's absolutely disgusting."

Mrs Pearson said she was in the block of seats next to where the explosion occurred. She said: "Well it was just at the actual final moment of the concert. Then all of a sudden this loud explosion, followed by a ton of smoke was coming up from the left of me.

"Then just absolute chaos. Disbelief, everybody running over each other not quite knowing what had gone on. Mad chaotic rush to nearest exit, lots of people crying and wailing. Really upsetting for everyone concerned. "There was people bleeding, and lots of people being separated, very scary, very upsetting but obviously we believe there has been fatalities. "It's just a terrible thing. Who could do this at a concert where there's children and families? Its just unbelievable." Mrs Pearson added: "I just feel for everybody that's been injured and those that have been killed."

Late on Monday night, Ariana Grande’s music label Universal Media Group put out the following statement:

We are deeply saddened to learn of tonight's devastating event in Manchester. Our thoughts and prayers are with all those affected by this tragedy.

Update 9: UK PM Theresa May has confirmed her election campaign has been suspended, issues following statement:

"We are working to establish the full details of what is being treated by the police as an appalling terrorist attack. “All our thoughts are with the victims and the families of those who have been affected.”

Update 8 : A second suspect device has been found near the Manchester Arena, and the Greater Manchester Police have carried out a "controlled explosion" in the Cathedral Gardens area near Manchester Arena.

There will be a controlled explosion in Cathedral gardens shortly if you hearing anything don't be concerned. — G M Police (@gmpolice) May 23, 2017

Officers carrying out a precautionary controlled explosion in Cathedral Garden confirm that it was abandoned clothing, not a suspicious item — G M Police (@gmpolice) May 23, 2017

Update 7 : From Mancester Police - 19 dead, around 50 injured...

Latest statement on incident at Manchester Arena pic.twitter.com/BEpLOan3dY — G M Police (@gmpolice) May 23, 2017

Update 6: NBC reports US officials briefed on Manchester incident say UK officials suspect it was caused by suicide bomber.

They used nail bombs at a kids concert in Manchester pic.twitter.com/oghHJDw0Hd — Tommy Robinson (@TRobinsonNewEra) May 22, 2017

Update 5 : Shocking first person description of the carnage (via Facebook)

Just out of The Ariana Grande Concert in Manchester,I thought we would leave seconds before the last song finished in order too get home quicker instead of waiting longer for a taxi,As we where leaving a bomb or explosion went off centimetres infront of me. Peoples skin/blood&Feces where everywhere including in my hair & on my bag,I'm still finding bits of god knows what in my hair.I am fine & back in my hotel I hope everyone involved and in front of me is okay.We are being told it was a balloon/sound system but I can assure you it was not,You never ever expect these things too happen too you but this proves it can happen too anybody. That sound,The blood & those who where running around clueless with body parts & bits of skin missing will not be leaving my mind any time soon or the minds of those involved. Again, Hope everyone is alright I am very,Very lucky too be where I am just now I understand these images might be upsetting however I feel as though people should know what happened

Update 4: Sky News reports another bomb located at Manchester's Victoria Metro Station - emergency units rushing. Bomb disposal units have arrived at the 'active crime scene' at Manchester Arena.

Manchester's Victoria station, which backs onto the arena, has been evacuated and all trains cancelled. National Rail said in an online statement: "Emergency services are dealing with an incident at Manchester Arena. As Manchester Victoria is located near the arena, the station has been evacuated and all lines closed. "Trains are currently unable to run to / from Manchester Victoria. Some trains will be cancelled throughout or start / terminate at alternative stations. Disruption is expected to continue until end of the day."

British Transport Police confirmed the blast came from "within the foyer area of the stadium at 10.30pm this evening".

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Update 3: BBC is reporting that authorities are treating the explosion as a terror incident.

The North West Counter Terrorism Unit is treating the incident at #ManchesterArena as a possible terrorist incident. — Daniel Sandford (@BBCDanielS) May 22, 2017

"We were making our way out and when we were right by the door there was a massive explosion and everybody was screaming," Catherine Macfarlane told Reuters. "It was a huge explosion - you could feel it in your chest. It was chaotic. Everybody was running and screaming and just trying to get out of the area."

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Update 2: NBC News confirms the BBC's report that there are at least 20 dead - Eye witness on BBC says 20 to 30 people injured and dead in the box office area of Manchester Arena.

Senior national Counter-Terrorism officers are assembling in London. Early estimates put fatalities at #ManchesterArena in double figures — Daniel Sandford (@BBCDanielS) May 22, 2017

BREAKING: At least 20 dead, hundreds injured following possible explosion at UK's Manchester arena - NBC News https://t.co/9XohT1Z7IV — CNBC Now (@CNBCnow) May 22, 2017

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Update 1: British trainlines out of Manchester Victoria station are currently blocked.

The explosions can be heard in the following clip... (around 7 seconds in - look to the far left and notice the sudden light also)

If you look towards the left you see the explosion and hear the bang. I hope to GOD everyone is ok, and so glad Jess and Em are. #manchester pic.twitter.com/q81KHGEJ6E — Joe Gregory (@JoeAaronGregory) May 22, 2017

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As we detailed earlier, "two loud explosions" were reported this evening at Manchester Arena by people attending a pop concert by Ariana Grande in an event that Greater Manchester Police is now describing as 'serious' and involving a "number of confirmed fatalities":

Police statement on incident at Manchester Arena pic.twitter.com/gaKASukx9a — G M Police (@gmpolice) May 22, 2017

Members of the public have been advised to avoid the arena.

One Twitter user wrote: "Honestly worst night of my existence. Just kept running from Manchester Arena for my life."

Another added: “Just got out of Manchester arena after seeing Ariana perform. There was a loud bang when the lights came on & everyone ran out screaming.”

Here are videos of the scene from just after the explosion: