Some 30 residents have been forced to leave their homes after a burst water main in north London left some areas under about 40cm (16in) of water.
About 70 firefighters were deployed to the incident in Islington just before 22:00 BST on Sunday, where they used flood barriers and sandbags to divert flood water away from homes, London Fire Brigade (LFB) said.
The public is being urged to avoid the area around Canonbury Street, Essex Road, Elmore Street, Halliford Street and Ecclesbourne Road and to avoid driving through flood water.
Supplier Thames Water said it was “working to stop the flow of water from the burst pipe” and that it would then focus on locating the damage and fixing it.
The provider said addresses in some areas had no water supply on Monday morning, while others were experiencing low pressure.
It also warned that local traffic in the area would be affected and apologised for any delays to people’s journeys.