Two men are in hospital after being stabbed at London's Wireless music festival, Scotland Yard has said.
The attack happened at around 9pm 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.