Four fire engines and around 25 firefighters were called to a fire at a town house converted into flats on Cricklade Avenue in Streatham Hill.
Part of a three-roomed flat on the first floor of the building was damaged by fire. There were no reports of any injuries.
The Brigade was called at 0518 and the fire was under control by 0655. Fire crews from West Norwood, Tooting and Norbury fire stations attended the scene.
The cause of the fire is under investigation.