A helicopter feared crashed in Papua New Guinea's Southern Highlands with two Australians on board was flying with reduced visibility in low cloud, authorities say.
Rescuers are continuing to search for the wreckage of the missing Bell 206 chopper, operated by Hevilift Ltd, which went missing on Friday afternoon near Mt Hagen.
Three people - two Australians and a New Zealander - were reportedly on board, including the pilot. All are Hevilift employees.
The Singapore-based air charter company, which caters to mining and energy operators, says the helicopter issued a mayday call five minutes after taking off from an InterOil drill rig in conditions of low cloud and reduced visibility.
"Aircraft in the vicinity heard the distress call from the helicopter and the InterOil flight followers were made aware of the problem, it is believed, soon afterwards," group deputy managing director Colin Seymour said from Singapore on Saturday.
"A localised search using Hevilift helicopters ... commenced immediately but deteriorating weather meant the helicopters were unable to search for long before the weather and last light closed down the search."
It's believed the chopper was on its way to refuel.
Seven helicopters have been searching the area since first light on Saturday along with a Dornier 328 fixed-wing plane dispatched from Australia. The Dornier is specially equipped to pick up electronic signals.
Hevilift said on Saturday afternoon that weather conditions during the search had improved to become "favourable".
No rescue beacon signals have been detected from the "thickly forested" region where the chopper disappeared.
PNG aviation officials said the chopper was thought to have gone down at Kikori, a densely wooded and oil-rich settlement at the head of the Gulf of Papua, but they were yet to find any wreckage and could not confirm fatalities.
"It was coming in from one of the InterOil sites ... to Mt Hagen," the head of civil aviation safety in PNG, Yaqub Amaki, told AAP.
"At the moment we don't know the status of the three."
The PNG adviser to the New Zealand Defence Force, Lieutenant-Colonel Richard Taylor, said the search would be difficult because to the rugged terrain which he likened to "a jungle version of the (NZ) Southern Alps".
Lieut-Col Taylor said there were a large number of aircraft in the area transporting ballot boxes, papers and officials for the ongoing national elections and "some of those will be able to be used for searching for the wreckage".
Earlier on Saturday, a spokesman for New Zealand's Ministry of Foreign Affairs confirmed that a Kiwi was on board the helicopter.
Mr Seymour said the company would not release the names of the two missing pilots and the aircraft engineer, saying it was in close contact with the families.
The Australian and New Zealand high commissions in Port Moresby were offering consular assistance to the men's families.
"We're in touch with the company," said Australia's deputy high commissioner Margaret Adamson.
Hevilift's group managing director, Paul Booij, was on his way to Mt Hagen on Saturday.