Ten fire engines and around 70 firefighters responded to a fire on Upper Tulse Hill, Lambeth.
A second-floor flat was destroyed by fire and part of the roof was also damaged. There were no reports of any injuries.
The Brigade received the first of 15 calls reporting the fire at 1421. Crews from Brixton, Tooting, Forest Hill and surrounding fire stations were mobilised to the scene. Firefighters had the fire under control by 1540.
The cause of the fire has been recorded as undetermined.