One person has now been released from hospital after being stabbed at the Wireless music festival in east London.
Two people were attacked during the event this weekend.
One man is in critical condition in hospital after a double stabbing at the Wireless music festival in east London on Sunday night.
The man, in his 20s, was stabbed at around 9pm at the Queen Elizabeth Olympic Park in Stratford, police said.
Another man is in non-life threatening condition in hospital.
Police added that no arrests has been made so far and that detectives were continuing their investigations.
According to the Wireless Festival website, US superstars Justin Timberlake and Jay-Z were due to perform on the main stage at the time that police said the incident took place.
Backstage at the Wireless music festival, Conor Maynard talks about how "nervous" he was opening the main stage.
Rap superstar Jay-Z declared he "likes" London as he headlined the Yahoo! Wireless Festival on its second night, at the Queen Elizabeth Olympic Park in east London.
He took to the stage for a solo show after joining Justin Timberlake for a rendition of their hit Suit And Tie on Friday night.
Jay-Z, in a crisp white shirt, black trousers, Nike trainers and a thick gold chain, said: "I feel the love tonight. I like it out here. I feel beautiful and I feel your energy.
"I appreciate it. You've been an incredible audience tonight."