Firefighters were called to a fire at a flat on Wivenhoe Close in Peckham.
Part of a four-roomed flat on the second floor of a three-storey block was damaged by the fire. Three people were treated on scene for minor smoke inhalation by London Ambulance Service crews.
The Brigade was called at 1139 and the fire was under control by 1219. Fire crews from New Cross and Old Kent Road fire stations were at the scene.
The Brigade's fire investigation team believe the fire was caused by an electrical event within an extraction unit.