A woman had to be led to safety after a fire thought to be caused by a carelessly discarded cigarette.
The fire happened in Byrne Road, Balham, on Saturday morning and badly damaged the ground floor flat.
The occupant was helped to safety by her upstairs neighbours, who had been alerted by a smoke alarm.
Two fire engines and about 10 firefighters from Tooting fire station attended at about 10.30am and it took an hour to get under control. Investigators believe a poorly extinguished cigarette was the cause.
London Fire Brigade's head of fire investigation Charlie Pugsley, said: "Thanks to the quick action of her neighbours the lady involved in this fire managed to escape, but if you are a smoker it is vital that you take extra care.
"Fires caused by smoking materials – including cigarettes, roll-ups, cigars and pipe tobacco – result in more deaths than any other type of fire. Last year around three fires a day in London were linked to smoking and half of accidental fire deaths were related to careless disposal of cigarettes.