Eight fire engines and around 60 firefighters were called to a fire at a maisonette on Barrington Road in Lambeth.
Firefighters tackled a blaze in two maisonettes on the fifth and sixth floor of an 11 storey building, both were significantly damaged by the fire. Around 30 people left the building before the Brigade arrived. Two men and one woman were treated at the scene by London Ambulance Service crews before being taken to hospital.
The Brigade's Control Office took 25 calls about the fire.
The Brigade was called at 1245 and the fire was under control by 1447. Fire crews from Brixton, Clapham, West Norwood, Battersea and crews from the surrounding areas attended the fire.
The fire is believed to have been accidental and caused by a discarded cigarette coming into contact with items stored on a balcony.