Four fire engines and around 25 firefighters tackled a fire at a flat on Ballards Lane in North Finchley.
Most of a four roomed flat on the first floor of a three storey mixed-use building was damaged by the fire. One woman who left the building before the arrival of the Brigade was taken to hospital by London Ambulance Service crews.
The Brigade was called at 1531 and the incident was over for firefighters at 1649. Firefighters from Finchley, Mill Hill, Hendon and West Hampstead Fire Stations attended the scene.
The cause of the fire is under investigation.