Four fire engines and around 25 firefighters were called to a fire at a food and wine shop on Chicheley Street in Lambeth.
Most of a ground floor shop at the bottom of a ten-storey, mixed-use development was damaged by fire.
Firefighters wearing breathing apparatus encountered heavy smoke through the building stairwell as they entered to tackle the blaze. One woman was led to safety from the first floor stairwell by fire crews. A second woman left the building before the Brigade arrived. Both were treated for smoke inhalation by London Ambulance Service crews at the scene.
Around 50 people from properties above the shop left the building before the Brigade arrived.
Station Officer Craig Abbott, who was at the scene, said: "On arrival we found a well-developed fire resulting from an explosion in the shop, and heavy smoke.
"Our crews worked hard to stop the blaze spreading into the upper floors of the block."
The Brigade was called at 1547 and the fire was under control by 1726. Fire crews from Lambeth and Soho fire stations attended the scene.
The Brigade's Fire Investigators believe the fire was accidental and caused by leaking lighter fluid that was ignited by a heater.