The privately owned aircraft is believed to have left Milton Keynes with five on board en route to Dublin
A helicopter with five people on board has gone missing over the Irish Sea.
A spokesman for the UK Coastguard said it was coordinating a search operation in the Caernarfon Bay area of North Wales.
Radar contact with the twin squirrel red helicopter was lost this afternoon and the UK Coastguard was asked to start a search operation at 4.15pm.
The privately owned aircraft is believed to have left Milton Keynes at around 11:30am on its way to Dublin and the its last communication was received just after 12pm.
Two search and rescue helicopters are involved in the search, which is being coordinated by the UK Coastguard.
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 any 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."
Irish Coastguard spokesperson Declan Geoghegan said air traffic control in the UK had contacted the Coastguard to ascertain whether Irish emergency services had any information on the helicopter’s whereabouts.
The Irish Coastguard has been undertaking a "communications search" on maritime frequency bands to try and locate the aircraft - and is ready to support the search if requested to do so.
A UK Coastguard spokeswoman said the search was being adversely affected by poor weather conditions.
She said: "There is quite poor visibility which is hampering the search efforts. There is a lot of low cloud coverage."
The search is still ongoing.