Thames Water crews are on-site working to repair the pipe, but the complexity of the damage means the work is expected to take several days.
The road closure spans both directions between St Nicholas Road and Kashgar Road.
Diversions are in place for all traffic, including buses. Routes 96, 99, 177, 180, 422, 469, and the N1 night service are affected, with detours now operational.
Drivers and public transport users are advised to allow extra time for their journeys as congestion in the area is likely.
The closure is necessary to ensure the safety of workers and the public while repairs are underway.
The exact location of the repair site is marked on What3Words as home.latter.slope.
Thames Water has apologised for the disruption and reassured residents that restoring the water supply and reopening the road are top priorities.
Updates on the progress of the repairs and traffic diversions will be provided on their website as the situation develops.
