Anglesey map The closure has caused an eight-mile diversion
The main road between Menai Bridge and Beaumaris on Anglesey has closed after a rock became displaced on the embankment above it, causing an eight-mile diversion.
The council closed a stretch of the road between Cichle Hill and Gallows Point from 18.00 GMT on Tuesday for safety reasons.
Diversions are in place on the A5025 to Pentraeth and the B5109 to Beaumaris.
The council is hoping to reopen the road later on Wednesday.
The diverted route is not accessible by HGVs because of a low bridge.