Four fire engines and around 25 firefighters were called to a fire at a flat in Finchley Road, Golders Green.
Half of a four-roomed flat on the third floor was damaged by the fire and a small part of the roof was also damaged. There were no reports of any injuries.
The Brigade was called at 1852 and the fire was under control by 1945. Fire crews from West Hampstead and Finchley fire stations attended the scene.
The cause of the fire is under investigation.