Four fire engines and 21 firefighters and officers were called to a fire at a house in Modbury Gardens, Belsize Park.
Part of the ground floor of the property was damaged by fire.
One woman left the house before the arrival of the Brigade and was taken to hospital by the Helicopter Emergency Medical Service (HEMS).
The Brigade was called at 2229 and the fire was under control at 2319. Fire crews from Kentish Town, Euston and West Hampstead fire stations attended the scene.
The cause of the fire is under investigation.