Five fire engines and around 35 firefighters were called to a restaurant with flats above on London Road in Croydon.
Part of the ground floor restaurant was damaged by fire. One man was treated on scene by London Ambulance Service crews.
The fire was discovered by two members of staff who noticed smoke coming from the rear of the kitchen and called the Brigade.
The Brigade’s Fire Investigators believe the fire was caused by heat radiating from a wok fire, which heated the stainless steel extractor hood and caused the timber frame above it to ignite.
A London Fire Brigade spokesperson said: “Cooking with hot oil can be really dangerous, as it can easily overheat, so it’s important to keep an eye on it at all times. If the oil starts to smoke, it’s too hot. Turn off the heat and leave it to cool.
“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.
“It is also a timely reminder to never to try and tackle a fire yourself. Our message if a fire breaks out is simple – get out, stay out and call 999.”