Four fire engines and around 25 firefighters tackled a maisonette fire on Tilson Gardens in Clapham.
Part of a split-level maisonette on the fourth and fifth floors of a residential block was damaged by fire. Three people left the building before the Brigade arrived and were treated on scene by London Ambulance Service crews after suffering from smoke inhalation.
The fire is believed to have been accidental and caused by a fan heater.
A London Fire Brigade spokesperson said: "It’s absolutely vital that heaters are kept well away from curtains, furniture, paperwork and are never used to dry clothes. Always sit at least a metre away from the heater as it could set fire to your clothes or your chair. Supervise children carefully and position a heater where it won’t be knocked over and away from pets.
"Firefighters recommend that you have a look at our online Home Fire Safety Checker to make sure there are no hidden hazards in your home. The online tool will ask you a series of questions that will help us work out the level of risk in your home, or the home of someone you care for. It only takes a few minutes to get tailored advice to keep yourself and loved ones safe from fire.”
The Brigade’s Control Officers took the first of three calls to the fire at 0817 and mobilised crews from Brixton, Clapham and Tooting fire stations to the scene. The fire was under control by 1044.