A spokesman for the UK Coastguard said it was coordinating a search operation in the Caernarfon Bay area of North Wales.
The privately owned twin squirrel red helicopter is believed to have left Milton Keynes yesterday (Wednesday) en route to Dublin, via Caernarfon Bay.
The spokesman said radar contact with the helicopter was lost on Wednesday afternoon and the Coastguard was notified to start a search operation at 4.15pm.
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.”
A spokeswoman for the Coastguard added 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.
More on this as we get it.