A man has been stabbed in the neck at a Jessie J party.
The victim, believed to be in his 30s, is in a "serious condition" in hospital after being attacked with a broken bottle following the 'Price Tag' singer's performance at a bash sponsored by phone company BlackBerry in London last night.
Jessie, 24, finished her set at the Pulse underground nightclub off Southwark Street at around 11.40pm and guests were heading to the cloakrooms when a fight is believed to have broken out.
Benjamin Cohen, Channel 4's technology correspondent, was at the gig and says one of the door men got covered in blood.
He told the Daily Telegraph newspaper: "Everyone tried to leave at the same time but the organisers weren't geared up for it and there was a huge rush to get to the cloakroom.
"People were crying and quite a lot were being sick, whether from the blood or the alcohol."
One man was arrested and is in police custody while the 450 revellers at the event were kept in the club until 1.50am while police launched their investigations.
A source told The Sun newspaper: "It happened in the main area to the right of the stage where the bar is after Jessie J had performed.
"VIP, celebs and everything cannot leave until cops get the statements they need. Everyone is really shocked."