WARNING THIS VIDEO CONTAINS STRONG LANGUAGE

A disturbing video posted online has captured the terror inside the Manchester Arena at the exact moment a blast rocked the venue.

The 19 second clip, which appeared on Twitter, gives a horrifying eyewitness account of when an explosion killed nineteen people at the Ariana Grande concert.

In the video a loud bomb-like explosion is clearly heard before a woman screams: "Oh My God. What has happened?"

Greater Manchester Police Chief Constable Ian Hopkins said the blast is being treated as a "terrorist incident until we have further information".

If found to be a terrorist attack it would the worst atrocity in the UK since 56 people were killed in the 7/7 London bombings in 2005.

As investigators begin to piece together what happened, here is a summary of events so far:

:: Police said around 50 people were injured, while North West Ambulance Service said 59 casualties had been taken to six hospitals around the city.

:: Officers carried out a controlled explosion on a second suspect item, which they later said was abandoned clothing.

The Herald:

:: Home Secretary Amber Rudd has described it as a "barbaric act", while Prime Minister Theresa May said her thoughts are with those affected by the "appalling" incident and will chair a Cobra meeting on Tuesday.

:: A spokesman for the American singer said she is uninjured.

Witnesses reported hearing a "huge bang" at around 10.30pm, as fans were leaving the arena shortly after the show finished.

One fan, Majid Khan, 22, described how the explosion happened: "A huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena.

The Herald:

"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."

Oliver Jones, 17, who attended with his 19-year-old sister, said: "The bang echoed around the foyer of the arena and people started to run.

"I seen people running and screaming towards one direction and then many were turning around to run back the other way."

The area around the arena was swamped with police and emergency services and approach roads were closed.

Manchester's Victoria station, which backs on to the arena, was evacuated and all trains and trams cancelled.

National Rail said: "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 said: "Officers are at Manchester Arena following reports of an explosion within the foyer area of the stadium at 10.30pm this evening."

The ambulance service warned people only to call "for life-threatening emergencies" and said a "large number of resources" were at the incident.

Manchester Fire and Rescue described the incident as "utterly heartbreaking" and asked people not to dial 999 "unless you really need us".

Manchester Arena said the explosion happened "outside the venue in a public space".

"Our thoughts and prayers go out to the victims," it said.

Sir Richard Leese, leader of Manchester City Council, said: "This is an absolutely horrifying incident and our thoughts are with everyone affected, especially those who have lost loved ones or been injured and traumatised.

"If it is confirmed this was a terrorist attack it is a monstrous act but also a deeply futile one. Manchester is a proud and strong city and we will not allow those who seek to sow fear and division to achieve their aims.

"We give heartfelt thanks to our emergency services for their response and council staff are doing all they can to support."

Joseph Carozza, a representative from Grande's US record label, confirmed that the singer is okay.

North West Ambulance Service said it has taken 59 casualties to various hospitals and treated a number of walking wounded at the scene.

Mr Hopkins said: "At around 10.33pm we received reports of an explosion at Manchester Arena in the city centre.

"This was at the conclusion of the Ariana Grande concert.

"Currently, we have 19 people confirmed to have lost their lives in the explosion and around 50 casualties that are being treated at six hospitals around Greater Manchester.

"My thoughts are very much with those who have been injured and lost their lives and their loved ones at this terrible time, we are doing all we can to support them.

An emergency number was established for those concerned about loved ones - 0161 856 9400.

Mr Hopkins said: "We are currently treating this as a terrorist incident until we have further information, we are working closely with national counter-terrorism policing network and UK intelligence partners.

"This is clearly a very concerning time for everyone. We are doing all that we can, working with local and national agencies to support those affected as we gather information about what happened last night."