Four fire engines and around 25 firefighters tackled a fire at a takeaway restaurant on Kennington Road in Lambeth.
An extraction unit on a flat roof above the takeaway, along with ducting, was damaged by fire. Several people left the takeaway and flats above before firefighters arrived. There were no reports of any injuries.
The fire is believed to have been caused by the ignition of grease in the ducting system.
A London Fire Brigade spokesperson 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 at 0020 and the fire was extinguished by 0145. Crews from Lambeth, Dowgate and Soho fire stations attended the scene. A 32 metre turntable ladder was used at the scene as an observation tower, providing the Incident Commander with a greater situational awareness of the fire.