Six fire engines and 35 firefighters and officers were called to a fire at a restaurant with flats above in West End Lane, West Hampstead.
Part of a second floor flat and the roof were alight.
Station Manager Lee Walker, who was at the scene, said: "Crews worked hard to bring the fire under control.
"Traffic is heavy in the area as West End Lane has been closed.
"Firefighters are likely to remain on scene damping down into the evening."
The cause of the fire is under investigation.