Four fire engines and around 25 firefighters were called to a fire at a restaurant with offices above on South Molton Street in Mayfair.
Half of the fourth floor of a five-storey building was damaged by the fire. There were no reports of any injuries.
The Brigade was called at 0958 and the fire was under control by 1116. Fire crews from Soho, Euston and Paddington fire stations were at the scene.
The fire is believed to be accidental and caused by a fault with the computer network server unit.