Six fire engines and around 40 firefighters were called to a flat fire on Christchurch Avenue in Kilburn.
Most of a two-roomed flat on the third floor and part of the roof of the building were damaged by fire. There were no reports of any injuries.
The Brigade was called at 1348 and the fire was under control by 1432. Fire crews from West Hampstead, Willesden, North Kensington and Paddington fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.