Pembrokeshire County Council can confirm that Devonshire Drive, near St. Florence, closed on Tuesday from its junction with the B4318, north-east to its junction with the A478.
The closure is required so that drainage and carriageway reconstruction work can be carried out at various locations along the road.
The work is being carried out by the Pembrokeshire County Council's engineering works division.
The road is closed to through traffic, although pedestrian and vehicular access is being maintained.
Traffic wishing to travel in a north-east direction along Devonshire Drive will be diverted via the B4318 to Tenby, then the A4139 (Marsh Road), A4219 (Maudlins) and the A478 to Crane Cross and to a point north-east of the closure.
The arrangements are vice versa for south-west bound traffic.
The work should be completed in six to eight weeks.