Eight fire engines and around 60 firefighters were called to a flat fire on Sydenham Road in Croydon.
Most of the first floor and the roof of a terraced house converted into flats were damaged by fire. One person left the building before the Brigade arrived.
The Brigade's 999 Control Officers took 22 calls to the blaze.
Leading Firefighter Ryan Senior-Ellison, who was at the scene, said: "Crews arrived to find a well-developed fire in a flat on the first floor and flames coming from the roof. The fire produced a significant amount of smoke which was very visible in the surrounding area.
"Firefighters wearing breathing apparatus rescued one man from a flat on the ground floor of the building who was taken to hospital by London Ambulance Service crews.
"Crews worked incredibly hard to stop the fire from spreading to adjacent properties and prevented further damage."
The Brigade was called at 2323 and the fire was under control by 0107. Fire crews from Croydon, Norbury, West Norwood, Addington and Beckenham fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.