Ten fire engines and around 70 firefighters were called to a fire at commercial units with flats above on Walthamstow High Street.
The fire destroyed two shops and a takeaway restaurant. Two residents from the flats were led to safety by crews.
Firefighters believe the fire was accidental and caused by a build up of grease and cooking fat in the takeaway restaurant's extraction system.
A London Fire Brigade spokesperson said: "This fire was inside the ducting (extraction system).
"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."
Firefighters' top tips for restaurants and takeaways:
The Brigade was called at 2154 and the fire was under control by 0037. Crews from Walthamstow, Leyton, Tottenham, Leytonstone, Woodford, Homerton and Stoke Newington fire stations were at the scene.