Six fire engines and around 40 firefighters responded to a fire in an office block on West Hendon Broadway, Colindale.
Part of a conference room on the third floor, in a building of six floors, was damaged by the fire.
The Brigade's Control Room was called at 1753, and crews from Park Royal, West Hampstead, Hendon and surrounding fire stations were mobilised to the scene. Crews were able to bring the fire under control by 1846.
The cause of the fire is not yet known.