Four fire engines and around 25 firefighters tackled a fire on Boundary Row in Southwark.
Part of a room in the basement of a three-storey office building was damaged by fire. There were no reports of any injuries.
The Brigade was called at 1327 and the fire was extinguished by 1441. Crews from Lambeth, Soho and Dockhead fire stations attended the scene.
The fire is believed to have been caused by an electrical fault.