Four fire engines and 21 firefighters and officers were called to a fire at a house converted into flats in Chichele Road, Cricklewood.
Part of a four-roomed flat on the first floor was damaged by the fire. One woman left the property before the arrival of the Brigade. She was treated at the scene for smoke inhalation and taken to hospital by London Ambulance Service crews.
The Brigade was called at 1416 and the fire was under control at 1538. Fire crews from Willesden, North Kensington and Paddington fire stations attended the scene.
The cause of the fire is under investigation by the Metropolitan Police Service.