Some people had complained of poor security
One man was stabbed and two others were injured during a music awards ceremony in south-east London.
Organisers were forced to call off The Urban Music Awards ceremony at the O2 arena in Greenwich after violence broke out on Saturday night.
The stabbed man, who is 27, is in a critical condition in hospital. The other injured have been treated in hospital for minor injuries.
A 21-year-old man has been arrested and bailed in connection with the incident.
The Metropolitan Police said the 21-year-old was bailed late on Sunday night to return to a south London police station in January.
'Covered in blood'
Officers initially cleared the room immediately following the incident, but the audience was later allowed back in.
Andre Nevling, 24, said a woman sitting at his table was "covered in blood".
"Obviously the guy who got stabbed must have run straight past her and she's pretty shaken up," he said.
Mike Muller, 38, from London, said there was a lot of confusion and hysteria.
"The company I work for, Intensify Youth, were presenting an award.
"Our man was just about to go on stage and present the award when this happened.
"The irony is Intensify Youth is a project that aims to combat knife crime so this is really disappointing."
Police put a cordon in place outside the arena and guests were questioned before being allowed to leave.
The awards were being held in indigO2, a 2,350-capacity venue inside the O2 Arena.
Estelle, Adele, Leona Lewis, Dizzee Rascal and Duffy were among the performers nominated for awards, but it is not yet known which celebrities were in attendance.
Some people at the event said security was poor.
Natalie Williams, 32, said: "Before anything even happened I commented to my boyfriend, because we live nearby and come here a lot, and we usually get screened coming into the building. Tonight there was nothing."
Chris Miller, who was reviewing the awards for an online music guide, said people were wandering into the press room without a pass.
"Even when we were waiting outside in the press area for stars to arrive, it was a melee," he said.
"The security was so slack."
An O2 spokesperson said: "Nothing of this nature has ever taken place in the venue before and all the usual stringent security measures were in place.
"We are working closely with the police to understand how this happened. Our thoughts are with the victims of the attack."
In 2004, a woman was shot outside the Urban Music Awards when it was held at the Barbican Centre in the City of London.