Six people fled from a block of flats after fire broke out on the ground floor.
Firefighters were called to the blaze in Byrne Road, Balham, at about 7.15am this morning.
It was caused after someone living in the flat left a jumper on a lamp, causing the room to be filled with smoke.
Firecrews spent an hour putting it out, while about a quarter of the building was damaged.
The person living in the flat was sent to St George's Hospital with smoke inhalation.