Four fire engines and around 25 firefighters were called to a fire on Streatham High Road.
A small part of a cupboard in the basement of a shop was damaged by the fire. There were no reports of any injuries.
The fire is believed to have been accidental and caused by the unsafe disposal of smoking materials.
A London Fire Brigade spokesperson said: "We’d rather you didn’t smoke at all, but if you are a smoker, it’s absolutely vital you ensure your cigarette is completely out when you’ve finished smoking it.
“If you don’t, you risk causing a fire which could not only destroy your home, but also cost you your life.”
The Brigade was called at 1545 and the fire was under control by 1632. Fire crews from Tooting and Norbury fire stations were at the scene.
Safety advice for smokers: