Four fire engines and 21 firefighters and officers were called to a fire at a block of maisonettes in Colindale Avenue, Colindale.
More than half of a three-roomed maisonette on the ground floor was damaged by fire. Six people left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 0200 and the fire was under control at 0259. Fire crews from Hendon, Mill Hill and Stanmore fire stations attended the scene.
The cause of the fire is under investigation.