Six fire engines and around 40 firefighters were called to a fire at a shop with flats above on Bridge Street in Pinner.
Half of the second floor and half of the roof of a mid-terraced shop with flats above were damaged by fire. There were no reports of any injuries.
The Brigade was called at 1517 and the fire was under control by 1641. Fire crews from Harrow, Northolt, Ruislip and Stanmore fire stations were at the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.