Four fire engines and around 25 firefighters attended a fire in an office in East India Dock Road, Poplar.
A ground floor office in a mixed used building was partly damaged by fire. Twenty people left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 0241 and the fire was under control by 0336.
Fire crews from Poplar, Millwall, Shadwell and Whitechapel stations attended the incident.
The cause of the fire is under investigation.