Four fire engines and around 20 firefighters and officers were called to a fire at an office block under refurbishment in West Heath Road in Hampstead.
Part of the basement of the building was damaged by fire.
The Brigade was called at 1147 and the fire was under control at 1309. Fire crews from West Hampstead, Paddington, Willesden and Kentish Town fire stations attended the scene.
The cause of the fire is under investigation.