Firefighters have issued a candle safety warning and are urging people not to tackle fires themselves after a blaze at a house in Cavendish Road in Clapham.
A candle left on a windowsill of an open window is believed to have blown over and started a fire. The property had no working smoke alarms and the alarm was only raised after one of the occupants smelt smoke.
The occupants of the property unsuccessfully tried to extinguish the fire themselves before leaving the property and calling the Brigade.
Watch manager Guy Pedliham, who was at the scene, said: "The occupants of this property had a very lucky escape as it was purely by chance that one person was awake at the time the fire started.
"Not only had a candle been left unattended, but the property also had no working smoke alarms fitted. Every home should have a minimum of one smoke alarm fitted per floor of their home.
"The occupants also tried to extinguish the fire before calling the Brigade. Our advice would be not to tackle fires yourself and to leave it to the professionals. Get out, stay out and call 999 immediately."
Part of a small room in the loft area was damaged by fire.
One woman was treated for smoke inhalation at the scene before being taken to hospital by London Ambulance Service crews.
The Brigade was called at 0320 and the fire was under control at 0355. Two fire engines and around 10 firefighters from Clapham and Tooting fire stations attended the scene.