Four fire engines and around 25 firefighters were called to a fire at an office block on London Wall in the City.
A small part of a kitchen on the fourth floor was damaged by the fire. Around 26 people left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 0025 and the fire was under control by 0139. Fire crews from Dowgate, Whitechapel, Islington and Soho fire stations attended the scene.
The Brigade's fire investigators believe the cause of the fire was an electrical fault within a heater.