Four fire engines and around 25 firefighters were called to a flat fire on Macmillan Way in Tooting.
Part of a flat on the first floor of a four-storey block was damaged by the fire. One woman left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 1401 and the fire was under control by 1530. Fire crews from Tooting, Norbury, West Norwood and Wimbledon fire stations were at the scene.
The fire is believed to have been electrical and caused by resistive heating.