Ten fire engines and around 70 firefighters responded to a fire on Upper Tulse Hill, Lambeth.
The incident was located in a residential block of flats, consisting of three floors. Part of a second floor flat and a section of roof was alight. There are no reports of any injuries.
Traffic in the surrounding area is likely to be impacted as crews remain on scene into the evening.
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 is under investigation by the Brigade's fire investigation unit.