Eight fire engines and around 60 firefighters tackled a fire on Minster Road in Kilburn.
The fire occurred at a three-storey detached house converted into flats. A ground floor self-contained flat to the rear of the property was damaged by fire. One man left the flat before firefighters arrived and he was taken to hospital by London Ambulance Service crews. Five other people also left the building before firefighters arrived.
People in the area were advised to keep windows and doors closed due to the amount of smoke being produced.
Road closures were in place including on the A5 (Shoot-Up Hill) at the junction of Minster Road. Drivers were advised to find alternative routes with traffic disruption expected.
The Brigade's 999 Control Officers received around eight calls about the fire.
The Brigade was called at 1047 and the fire was extinguished by 1226. Crews from West Hampstead, Paddington, North Kensington and surrounding fire stations attended the scene.
The cause of the fire is under investigation.