Four fire engines and around 25 firefighters were called to a fire at a shop on Mitcham Lane in Tooting.
Most of a ground floor shop was damaged by fire. A man and a woman left a flat above the shop before firefighters arrived. There were no reports of any injuries.
The Brigade was called at 0204 and the fire was under control by 0354. Fire crews from Tooting, West Norwood and Mitcham fire stations attended the scene.
The cause of the fire is believed to have been electrical.