The A283 Steyning Road in Shoreham has been closed over fears the surface could collapse.
Police were called at 10.50am to reports of flooding on the road. The road was closed between the Clover Leaf roundabout at the A27 and the Red Lion pub at the junction with Upper Shoreham Road.
The road has been closed in both directions and is expected to remain shut for several days while a burst water main and the road are repaired.
Many roads across Berkshire are closed because of flooding.
Flash floods could bring worse disruption than seven years ago.