Four fire engines and around 25 firefighters were called to a fire at flats above a shop on Golders Green Road in Golders Green.
Part of a bedsit on the third floor of the three-storey block was damaged by the fire. There were no reports of any injuries.
The Brigade was called at 0431 and the fire was under control by 0544. Fire crews from West Hampstead, Hendon and Finchley fire stations were at the scene.
The cause of the fire is under investigation.