Footage from yesterday's Million Mask March reportedly shows Leicester Square after a smoke bomb was set off.
The Million Mask March happens every year and features thousands of people dressed in V For Vendetta (Guy Fawkes) masks, who protest against various social injustices.
The masks are also associated with the loose hacking collective Anonymous, who organised this year's event to protest against austerity and the surveillance state.
This year's march began peacefully in Trafalgar Square but by the end of the night at least 30 people had reportedly been arrested and several police officers had been injured.
