"A search of the Irish sea route is commencing this evening".
The privately owned helicopter carrying five people on board is believed to have left Milton Keynes en route to Dublin.
The UK Coastguard is coordinating search efforts off north Wales, while the Irish Coastguard is assisting with a communications search.
Radar contact was lost and a search operation was launched shortly after 4 o'clock yesterday afternoon.
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Two UK Coastguard helicopters were sweeping areas off the Welsh coast using infra-red camera technology for any signs of debris.
A spokesman said it had not been asked to supply any physical search and rescue assets as of 10pm. A Mayday Relay broadcast has been issued to all vessels travelling through the Irish Sea route to contact the Coastguard if they see anything.
A spokeswoman for the Coastguard said the search was being affected by weather conditions.
In a statement, the UK Coastguard confirmed that air, sea and land-based assets were involved in the search.
North Wales Police have also been notified of the search operation.
The Irish Coastguard's Dublin-based helicopter base is now without a search and rescue aircraft, since the crash of Rescue 116 in north Mayo in the early hours of March 14th.