Six fire engines and around 40 firefighters were called to a fire at a mid-terraced house converted into flats on Clifton Road in South Norwood.
Half of the basement and part of the ground floor of the building were damaged by fire. Firefighters rescued a woman from the rear basement window. She was taken to hospital by London Ambulance Service crews.
The Brigade was called at 0047 and the fire was under control by 0144. Fire crews from Woodside, Croydon, Beckenham, West Norwood, Norbury and Forest Hill fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.