Six fire engines and around 40 firefighters tackled a flat fire on York Hill in West Norwood.
Most of a two-roomed flat on the second floor of a residential block was damaged by fire. Two left the flat before firefighters arrived and around 30 further people left the building. A man was taken to hospital by London Ambulance Service crews.
The Brigade's 999 Control Officers took 14 calls to the blaze.
Station Commander Pat Ackroyd, who was at the scene, said: "Firefighters worked incredibly hard to quickly bring the fire under control.
"York Hill was partially closed whilst crews work to make the scene safe."
The Brigade was called at 0922 and the fire was under control by 1023. Fire crews from West Norwood, Brixton, Norbury and surrounding fire stations attended the scene.
The cause of the fire has been recorded as undetermined.