Four fire engines and around 25 firefighters tackled a fire in a flat in Leigham Court Road, Streatham.
Part of a second floor flat was damaged by fire. Firefighters wearing breathing apparatus rescued a child via an internal staircase. The child was taken to hospital by London Ambulance crews. A man and a woman left the building before crews arrived.
The Brigade was called at 1237 and the fire was under control by 1508. Crews from Lambeth, Norbury and Tooting Stations attended the incident.
The cause of the fire is under investigation.