Four fire engines and around 25 firefighters were called to a fire at a block of maisonettes on Woodbine Grove in Penge.
The call comes following reports of an explosion in the bedroom with the flat.
Part of a split-level six-roomed maisonette on the third and fourth floor of a four-storey block was damaged by the fire.
A man and woman left the property before the Brigade arrived. They were treated on scene for smoke inhalation by paramedics from London Ambulance Service.
The Brigade was called at 11.07am and the fire was under control by 12.02pm. Fire crews from Beckenham, Woodside and West Norwood fire stations were at the scene.
The cause of the fire is under investigation and is being investigated by specialist from the LFB