Four fire engines and around 25 firefighters tackled a fire at a hotel on Lanesborough Place in Soho.
Part of a circuit breaker within a switch room in the basement was damaged by the fire. There were no reports of any injuries.
The fire is believed to have been accidental and caused by an electrical fault.
The Brigade was called at 0618 and the incident was over for firefighters at 1220. Firefighters from Soho, Lambeth and Paddington fire stations attended the scene.