Two men were stabbed during Jay-Z and Justin Timberlake's performance at Yahoo! Wireless Festival.
The incidents occurred while the '99 Problems' rapper and the R&B singer were previewing their 'Legends of the Summer' tour on the main stage in London's Olympic Park on Sunday evening (14.07.13) to a crowd of around 80,000 fans.
Paramedics were alerted and one man was rushed to the hospital in a critical condition, while the other was in a satisfactory condition, according to the Met Police.
It is as yet unclear whether the attacks were connected, but both are said to have happened around 9pm. No arrests have been made in relation to the incident.
Justin and Jay-Z kicked off their hotly-anticipated two-hour set with 'Holy Grail', the lead single from Jay-Z's new studio album 'Magna Carta Holy Grail' and took it in turns to perform some of their biggest hits.
Rihanna stunned fans by making a brief appearance on stage to duet with Jay-Z for a rendition of their hit song 'Run This Town'.
Will.i.am, Rizzle Kicks, Big Sean, A$AP Rocky and Nas all performed during the final day of Wireless festival.