Firefighters were called to put out a blaze at a pizzeria in Clapham on Monday.
Four fire engines and around 25 firefighters were called to the takeaway pizza shop with flats above in North Street in the early hours of the morning.
Part of the ground and first floors of the building and part of the external extraction system were damaged by fire.
A man and a woman were treated on the scene by London Ambulance Service crews after suffering from smoke inhalation.
The fire is believed to have been accidental and caused by hot embers coming into contact with built-up grease in the extraction system above the pizza oven.
A London Fire Brigade spokesman said: “We’d like to remind restaurant and takeaway owners to ensure they don’t have dirty ducting.
“If you don’t clean the ducting in your extraction system regularly, you’re at a greater risk of ducting fires.
“You should also make sure you keep the hob, cooker hood and extractor fan clean too – built up fat and grease can ignite and cause a fire.”
The Brigade was called shortly before 3.30am and the fire was under control by just after 5am.
Fire crews from Clapham, Battersea, Brixton and Lambeth fire stations attended the scene.