A woman was rescued by firefighters after a flat fire in Saint Georges Road, Lambeth.
Part of an electrical intake room on the ground floor of the block was damaged by fire.
One woman was rescued from a first floor flat by crews wearing breathing apparatus. She was treated at the scene for smoke inhalation before being taken to hospital by London Ambulance Service.
The Brigade was called at 1226 and the fire was under control at 1328. Four fire engines and 21 firefighters and officers were called to the scene. Fire crews from Lambeth, Old Kent Road and Dowgate fire stations attended.
The fire is believed to have been caused by an electrical fault.