A road between Warrenpoint and Rostrevor in Co Down has been closed amid fears the route is about to collapse.
The emergency road closure of the Rostrevor Road near St Leonards is expected to cause significant disruption to traffic.
But road officials fear the road could cave in at any moment.
Transport NI said the road would be closed to all vehicles and pedestrians to "undertake emergency repairs to the sea wall and to allow the installation of a new culvert".
The body said it became "aware of a deterioration in the condition of the sea wall over the Easter holidays and following inspection the carriageway was reduced to one lane under traffic signal control".
"The area of instability in the wall is immediately adjacent to a large culvert ,which was due to be upgraded later this year, by Rivers Agency," it said.
"Transport NI and Rivers Agency have brought forward the replacement culvert works.
"They will be working together to complete the installation of a new reinforced concrete box culvert in the carriageway and the associated wall and protection structures."
The work is due to be completed by May 13 and diversions are in place during the closure period.
Meanwhile, there were significant traffic delays in west Belfast yesterday following a problem with the traffic lights at Kennedy Way.
It was reported that the lights were stuck on red on Kennedy Way towards Stockmans Lane roundabout leading to major tailbacks in the area.
Engineers were called to deal with the timing fault on the traffic lights, but there were reports of significant traffic problems with many people taking to social media to vent their frustration including one man who said it was a "total shambles".
