Scenes of chaos, confusion and terror were captured by music fans who had travelled to Manchester Arena simply to enjoy an Ariana Grande concert.
The American singer was nearing the end of her gig when an explosion struck in the foyer in what is being treated as a terrorist attack.
At least 22 people have died and and 59 injured.
A loud, dull bang can be heard on footage posted to social media followed by screaming.
Other videos show the chaotic scenes immediately after the explosion as people rush to make their way out of the 21,000-capacity venue.
Anyone seeking information on anyone who may have been in the area should ring the following number:
Manchester Arena said in a statement that the explosion took place outside the venue, suggesting any perpetrator did not enter the building.
Outside the venue emergency services rushed to the scene to deal the attack.
Armed police were also in attendance.
Grande, who was not injured, tweeted hours later:
Home Secretary Amber Rudd has said the Manchester explosion was a “barbaric attack, deliberately targeting some of the most vulnerable in our society”.
A suicide attack is suspected but no group or individual has claimed responsibility at this time.
The PM’s General Election campaign is being suspended following the fatal explosion, a Tory source has said. Other parties indicated they would follow.
The incident led to a nightlong search for loved ones as parents tried to locate their teenage children and groups of friends scattered by the explosion sought to find one another.
Taxi services offered to give stranded concertgoers rides home for free, and residents opened their homes to provide lodging for people who could not get home because public transport had shut down.
City officials said the true spirit of Manchester would shine through despite the horrendous incident, reports the Associated Press.
If the incident is confirmed as a terrorist attack it would be the deadliest in Britain since four suicide bombers killed 52 London commuters on three subway trains and a bus in July 2005.
“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.