Eight fire engines and around 60 firefighters were called to reports of smoke coming from the roof of a mixed-use commercial and residential building on Commercial Road in Aldgate.
Firefighters investigated and found steam and smoke travelling through the building's extraction system from the basement to the roof. Crews isolated the supply to a boiler in the basement. Around 30 people left the building before the Brigade arrived. There were no reports of any injuries.
There were road closures in place and people were encouraged to avoid the area.
The Brigade's 999 Control Officers took 10 calls to the incident.
The Brigade was called at 0831 and the incident was over for firefighters by 1038. Fire crews from Whitechapel, Shadwell, Shoreditch, Dowgate, Bethnal Green and surrounding fire stations attended the scene.