Two men are in hospital after being stabbed at London's Wireless music festival, Scotland Yard has said.
The attack happened at around 9pm on Sunday while headline acts Justin Timberlake and Jay-Z were performing in front of tens of thousands of people.
One man in his 20s is in a critical condition and the other man, also believed to be in his 20s, is in a stable condition, a police spokesman said.
No arrests have been made.
The three-day festival at the Queen Elizabeth park on the Olympic site came to a close shortly before midnight.