Firefighters have damped down hotspots in the extraction system of the café basement on Eversholt Street in Euston.
The basement has been severely damaged. The fire spread through the extraction system and slightly damaged the ground and first floors at the rear of the building.
Three people left the building before the Brigade arrived. Fortunately, no one was injured.
Eight fire engines and around 58 firefighters and officers from Soho, Kentish Town, Shoreditch, Euston, North Kensington and Stoke Newington fire stations attended the fire.
The Brigade was called at 0936 and the fire was brought under control at 1140.
The cause of the fire is under investigation.