Four fire engines and 21 firefighters and officers were called to a fire at a house converted into flats in Alexandra Close in Harrow.
Part of the first floor and the roof of the property were damaged by fire.
The Brigade was called at 1452 and the fire was under control at 1606. Fire crews from Harrow, Wembley and Ruislip fire stations attended the scene.
The cause of the fire is under investigation.