Five fire engines and around 30 firefighters tackled a fire in a building under construction on Hanover Street in Mayfair.
An electrical consumer unit in an electrical intake room in the basement was destroyed by fire. There were no reports of any injuries.
The Brigade was called at 0624 and the fire was extinguished by 0819. Crews from Soho, Euston and Lambeth fire stations attended the scene.
The fire is being treated as accidental.