Four fire engines and around 25 firefighters were called to a burst water main on Harrow Road in Wembley.
The road was flooded on Harrow Road and road closures were in place.
A London Fire Brigade spokesperson said: "Harrow Road was closed from the junction of Copland Road to the junction of Ealing Road. Drivers were strongly advised to avoid the area. The road closure was expected to be in place until lunchtime."
The Brigade was called at 0810 and the incident was over by 1105. Fire crews from Wembley, Park Royal and Northolt fire stations were at the scene.