A sea search is under way after reports that someone had been swept off rocks while fishing.
HM Coastguard is coordinating the response after an incident at Trearddur Bay, Anglesey, on Saturday.
A helicopter and RNLI lifeboats have been involved in the search which resumed at first light on Sunday.
Holyhead, Moelfre and Rhosneigr coastguard rescue teams were also called out along with Wales Ambulance Service and North Wales Police.
Andy Hodgson, from Trearddur Bay lifeboat station, confirmed crews were called at 19:05 BST on Saturday to “reports that someone had been swept off rocks while fishing”.
“Crews from both our inshore lifeboats searched until midnight, and began searching again at first light today, around 05:30.
“Both boats will continue the search today,” he added.
On Saturday evening, North Wales Police said there was a “serious police incident currently ongoing” at Ravens Point, Trearddur Bay.
“Members of the public are politely requested to leave / not to attend the area, as their presence is impeding on the operation there,” the force posted on Twitter, which has been rebranded as X., external.