Four fire engines and around 25 firefighters were called to a fire at a flat on Kensington Avenue in Thornton Heath.
Part of a flat on the first floor of a two-storey block was damaged by the fire.
The Brigade was called at 0002 and the fire was under control by 0137. Fire crews from Norbury and West Norwood fire stations were at the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.