Four fire engines and around 25 firefighters attended a house fire in Dalton Avenue in Mitcham.
The house, which had been converted into flats, was significantly damaged on the ground floor where one flat was completely destroyed by the fire.
The Brigade were called at 0256 and the fire was under control by 0500. Fire crews from Mitcham, Wimbledon, Tooting and Norbury attended the scene.
The cause of the fire will be investigated.