Four fire engines and around 25 firefighters responded to a fire at a block of flats on Fountain Road in Tooting.
Half of a three roomed flat on the first floor was damaged by the fire. Three people were taken to hospital by London Ambulance Service crews.
The cause of the fire is under investigation.
The Brigade was called at 1326 and the fire was under control by 1615. Firefighters from Tooting, Wimbledon and Wandsworth fire stations attended the scene.