Five businessmen are missing after the helicopter they were travelling in disappeared over the Irish Sea.
A massive air, land and sea search was launched last night for the privately-owned aircraft, which is thought to have crashed off the Welsh coast.
The UK Coastguard has been co-ordinating the search operation for the Airbus/Eurocopter Twin Squirrel helicopter, which vanished off radar in the Caernarfon Bay area.
It disappeared after 4pm yesterday, having left Milton Keynes bound for Westin airfield in Dublin.
The aircraft was last detected in the Caernarfon Bay area, less than 20km off the Welsh coast.
In a statement, the UK Coastguard confirmed that its air, sea and land-based assets were involved in the search.
Two UK Coastguard helicopters were sweeping areas off the coast using infra-red technology for any signs of debris.
It is understood that no mayday or distress call was received from the chopper, whose pilot was said to be very experienced.
"The UK Coastguard search and rescue helicopter based at Caernarfon has carried out an extensive land-based search of fields and airfields within the Caernarfon area and the helicopter based at St Athan has joined the search this evening," a spokesman said.
"A mayday relay broadcast has been issued to all vessels passing through the Irish Sea to contact the Coastguard if they have seen anything.
"A search of the Irish sea route is commencing this evening."
North Wales Police have also been notified of the search operation and has established a search plan.