A man is missing off the Doonbeg coast in Co Clare.
It is believed he was fishing at the time and the alarm was raised on Saturday morning.
The Shannon-based Coastguard search and rescue helicopter was sent to the scene.
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The Kilkee and Doolin units of the Coastguard is also assisting in the operation.
Gerard O'Flynn from Coastguard operations says divers may join the search later.