Four fire engines and around 25 firefighters were called to a fire at a takeaway on High Road in Willesden.
Part of the ground floor was damaged and a small part of a flat on the first floor was also damaged.
The fire is believed to have been accidental and caused by a charcoal grill igniting the restaurant's ducting.
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 2039 and the fire was under control by 2343. Fire crews from Willesden, Park Royal and Wembley fire stations were at the scene.