Six fire engines and around 40 firefighters were called to a fire at a house converted into flats on Asylum Road in Peckham.
The ground and first floors of the building were destroyed by fire and part of the ground floor of a neighbouring property was also damaged by the blaze. One woman was taken to hospital by London Ambulance Service crews after suffering from smoke inhalation.
Station Commander David Bracewell, who was at the scene, said: "Crews worked quickly to bring the fire under control. Two people left the building before the Brigade arrived."
The Brigade's 999 Control Officers took 15 calls to the fire.
The Brigade was called at 1559 and the fire was under control by 1649. Fire crews from Old Kent Road, Soho, Peckham, Dockhead, Greenwich and Brixton fire stations attended the scene.
The cause of the fire is under investigation.