Four fire engines and around 25 firefighters were called to reports of smoke in a basement on Canada Square, Canary Wharf.
A small fire in the basement of an office block was out before the Brigade arrived. One thousand people left the building before the arrival of the Brigade.
The Brigade was called at 1430 and fire crews from Millwall, Poplar, Plaistow, and East Greenwich fire stations attended the scene.
The cause of the fire is under investigation.