Four fire engines and around 25 firefighters tackled a fire on Evenwood Close in Putney.
Half of a flat on the second and third floors of a four-storey block of flats was damaged by fire. One man was treated at the scene by London Ambulance Service for smoke inhalation. Around 30 people left the building before firefighters arrived.
The Brigade was called at 0344 and the fire was extinguished by 0629. Crews from Wandsworth, Fulham, Battersea and Chelsea fire stations attended the scene.
The cause of the fire is under investigation.