A spokeswoman for the Coastguard said the search was being affected by weather conditions.
She said: "There is quite poor visibility which is hampering the search efforts. There is a lot of low cloud coverage."
But, she said the search was still ongoing.
A helicopter, bound for Dublin with five people on board, has gone missing at sea.
The privately owned twin squirrel red helicopter is thought to have left Milton Keynes earlier today, en route to Dublin via Caernarfon Bay.
The UK Coastguard is currently co-ordinating a search and rescue operation for the helicopter, which has five people on board.
There are currently two helicopters assisting the search, one from South Wales and one from North Wales.
UK coastguard is coordinating a search off Wales for helicopter which was bound for Dublin - 5 passengers on board https://t.co/jNgT1vpiUf
— Eoin English (@EoinBearla) March 29, 2017
Radar contact was lost earlier this evening and after contacting all airbases, the UK Coastguard were notified at 4.15pm.
The North Wales Police have also been notified.
UK Coastguard Duty Commander Peter Davies said: "We have established a search plan between Caernarfon Bay and the shore of Dublin and currently have two Coastguard helicopters searching the route.
"We are in the process of contacting all the vessels in the Irish Sea that were in the vicinity around midday and we are continuing Mayday broadcast action for any vessels currently in the area to contact us if they have further information.
"At the moment we are appealing to these vessels and to the public that if they have seen a twin squirrel red helicopter to please contact 999 and ask for the Coastguard."