Police are in a standoff with two men who are refusing to come down from the roof of a building in Kilburn.
Armed police are on the scene in Kingsgate Road as a precaution, after a person reportedly saw one of the men carrying a gun.
Lin Paris, who filmed this video of the men, told ITV London that she saw one of them performing a handstand before he walked across the roof like an 'acrobat'.
The pair were chased by officers who saw them tampering with a bike in nearby Mazemot Avenue at 5:11pm on Tuesday.
The police helicopter is being used to help the live operation.
Roads in the area are currently closed.