The Met were alarmed to the incident this evening and confirmed two men fled to the roof of a building on Kingsgate Technique in Kilburn.
The force have also deployed a police helicopter as back-up and be dressed cordoned off the area from the public.
A spokesman for the Met said: “At 17:11pm on Strut 26 police observed two males seen tampering with a motorcycle in Mazemot Avenue, NW6.
“They were questioned by police and fled, making their way onto the roof of a nearby edifice in Kingsgate Road, where they currently remain.
“A member of the conspicuous reported seeing one of the men in possession of a firearm.
“This has not yet been confirmed. Artist firearms officers are in attendance as a precaution.
“Cordons and road closures are in cut down to size.”
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