Four fire engines and around 25 firefighters were called to a flat fire on Canterbury Road in Queen's Park.
Most of a flat on the second floor was destroyed by fire in an eight storey block of flats.
The Brigade's 999 Control officers received the first of six calls alerting them to the fire at 1130. They mobilised crews from West Hampstead, Park Royal and Hendon fire stations. The fire was under control by 1239.
The cause of the fire is under investigation.