The B1127 near Southwold has been closed for emergency repairs after it was damaged by "extensive" flooding.
Suffolk Highways has confirmed the road has been sealed off at the junctions with Cove Bottom and Easton Lane, north of Reydon.
Motorists have been advised to follow a diversion route along the A12 to avoid the roadworks.
Flood warnings have been issued by the Environment Agency in the Southwold area recently as experts warned tides could be more than 2 metres higher than normal.
A Suffolk Highways spokesman said: "The reason for this closure is due to road damage caused by extensive tidal flooding which cannot be seen through flooded water.
"This road closure is in place to support the Environment Agency and further prevent additional damage to their assets beneath the carriageway. Repairs must be completed to both the drainage valves and the road before the closure can be removed.
"Regular inspections will be undertaken by our teams, and we will provide updates on timescales for repairs as they become available.
"We would like to apologise for any disruption this will cause, and we will keep you updated as best as possible."
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