Eight fire engines and 58 firefighters and officers were called to a fire at a restaurant and offices on Haymarket in SW1Y.
All of the ducting from the basement to the fifth floor and part of the ducting on the ground, first, second and third floor were damaged.
Three people left the property before the Brigade arrived and seven people were evacuated by firefighters. There were no reports of any injuries.
The Brigade was called at 0810 and the fire was under control by 1556. Fire crews from Soho, Lambeth, Islington, West Hampstead, Stoke Newington and Euston fire stations attended the scene.
The cause of the fire is under investigation.