Fire crews were called to a basement fire in Thornton Heath last night.
Two appliances from Norbury and one from Croydon were sent to the property in Bensham Lane at about 10.40pm.
The electrical intake cupboard in the house which has been converted into eight flats, caught alight and set fire to under the stairs.
The occupants of the basement flat had escaped uninjured, getting out through the back windows by the time firefighters arrived.
The rest of the house was also evacuated as a safety precaution.
A spokesman for the crew said: "We managed to contain it to 10 percent of the basement.
"It was difficult putting out a fire when there were live electrics, but the team did very, very well and the blaze was under control within 20 minutes."
No-one was injured, but the basement flat was badly damaged by the smoke.
The firefighter added: "The property had a hard wired smoke alarm system which alerted the occupants.
"It was lucky the flat was sitting on a slope, the rear of the flat was on the ground level, which meant they were able to get out the back window.
"If they had not escaped it is likely they would have suffered from smoke inhalation."
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