Four fire engines and around 25 firefighters were called to reports of a fire at a commercial property on Aldersgate Street in Islington.
Crews made the scene safe after discovering a blown transformer in an electrical unit in the basement. Around 100 people left the building before the arrival of the Brigade. There were no reports of any injuries.
The Brigade was called at 0939 and the fire was under control by 1044. Firefighters from Shoreditch, Islington, Soho, Euston and Bethnal Green fire stations attended the scene.