Crews rescued four people after a fire at the rear of a shop with flats above in Upper Tooting Road, Tooting Bec.
Six fire engines and 35 firefighters and officers were called to the blaze in a timber shed in the rear yard of the ground floor shop.
The shed was destroyed and part of the ground floor of the shop and the loft space of a terraced house backing onto the site were also damaged.
Crews wearing breathing apparatus used ladders to rescue three women and a man from a flat roof. One person was taken to hospital by London Ambulance Service crews.
Gas cylinders were involved in the fire and crews worked to cool the cylinders as they can explode when exposed to heat.
The Brigade was called at 1232 and the fire was under control at 1426. Fire engines from Tooting, Croydon, West Norwood and Norbury fire stations attended.
The cause of the fire is under investigation.