A concert by U.S. rapper Nas (search) was stopped after a gunman apparently opened fire in the London venue where he was performing, British police said Tuesday.

No one was injured in the incident at the Brixton Academy in south London late Monday, the city's Metropolitan Police force said.

The Evening Standard newspaper, however, reported that several people were hurt as panicked fans rushed to leave the concert, but didn't give any details.

Officers believe a gunman fired two shots at the ceiling, a police spokeswoman said, adding that Nas stopped performing immediately and organizers evacuated the venue. Police retrieved two bullets and two casings from the scene, she said.

No one was arrested in connection with the incident and the Metropolitan Police's Operation Trident — which probes violence within the black community — will take over the investigation, the spokeswoman said.

Brixton Academy spokeswoman Louise Kovacs said the venue was evacuated following consultation with police. She said there is "a high level of security" at every event at the concert hall, which can hold about 2,500 fans.

More than 100 security staff were working at Monday's show and concertgoers passed through scanning and security checks at the entrance to the venue, Kovacs added.