Eight fire engines and 58 firefighters and officers were called to a fire at a residential care home in Burnell Road, Sutton.
A second floor flat was destroyed by fire. Nineteen people left the premises before the arrival of the Brigade. Firefighters wearing breathing apparatus led two men and one woman to safety. They were treated at the scene by the London Ambulance Service.
The Brigade was called at 0659 and the fire was under control at 0818. Fire crews from Sutton, Mitcham, Wallington, Nobury, and Tooting fire stations attended the scene.
The cause of the fire is under investigation.