Five fire engines and around 30 firefighters and officers were called to flooding in Cecil Road in Harrow.
A burst water main caused flooding to a depth of approximately 1.5 metres. The water main was isolated and the water was pumped and drained away.
Around 100 office staff and three residents from a block of flats were evacuated as a precaution.
The Brigade was called at 1055 and the incident was over for firefighters at 1454. Fire crews from Harrow, Stanmore, Northolt and Ruislip fire stations attended the scene.