Four fire engines and around 25 firefighters were called to a fire at a restaurant with flats above on Blandford Road in Marylebone.
Part of the ducting on the ground floor of the building was damaged by the fire and part of the external ducting from the first to the fourth floor was damaged.
Around 15 members of staff and 15 customers left the building before the arrival of the Brigade. There were no reports of any injuries.
A London Fire Brigade spokesperson said: “This is a timely reminder to restaurant and take-away owners to always make sure their extraction systems are kept clean as a build up of fat and grease within the filters can lead to a fire.”
The Brigade was called at 1334 and the fire was under control by 1453. Fire crews from Paddington, Kensington, Euston and Soho fire stations attended the scene.
The Brigade's fire investigators believe the cause of the fire was a fault in a pizza oven which caused a build up of gas during a short power cut, which ignited when the power supply was reinstated.