Four fire engines and around 25 firefighters were called to a shop fire on Denmark Street in Camden.
A consumer unit in the basement of a shop under construction was destroyed by fire. There were no reports of any injuries.
The Brigade was called at 1900 and the fire was under control by 2054. Fire crews from Soho, Euston and Dowgate fire stations were at the scene.
The fire is believed to have been accidental and caused by an electrical event in a consumer unit.