Two people were taken to hospital with smoke inhalation after fire broke out.
Firefighters were called to Elspeth Road, Battersea, at 3am this morning.
People living in the flat smelt smoke and alerted the fire brigade.
A fire was discovered in the basement of the building, believed to have been caused by an extractor fan.
It took firefighters about two hours to put out the flat, which had smoke alarms fitted but with no batteries.
The occupants were taken to St George's Hospital.
Smoke damaged the flat, while the basement was wrecked in the fire.
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