Four fire engines and around 25 firefighters were called to a flooding on Spencer Road in Harrow.
Approximately 500 metres of the roadway was flooded to a depth of 150 millimetres after a water main burst. There were no reports of any injuries.
A London Fire Brigade spokesperson said: “Crews used sand bags to prevent flooding to nearby properties.
“Road closures were put in place as the water main supply was isolated and the water was drained away.
"Disruption to roads continues, so we kindly ask locals to avoid the area.”
The Brigade was called at 2148 and the incident was over for firefighters by 0038 (Thursday). Fire crews from Harrow, Stanmore and Northolt fire stations attended the scene along with Thames Water and the Metropolitan Police Service.