Four fire engines and 21 firefighters and officers were called to investigate a smell of smoke coming from a generator room in the basement of the Gherkin at St Mary Axe this morning.
A fuse in a transformer had burned out.
The Brigade was called at 0838 and the incident was over at 0942. Crews from Whitechapel, Dowgate, Shadwell and Dockhead fire stations were at the scene.