SEVEN Victorians and two Queenslanders setting off to walk the Kokoda Track are among 13 people aboard a plane feared to have crashed in rugged terrain in Papua New Guinea.
Foreign Minister Stephen Smith said there were fears for those aboard Airlines of Papua New Guinea flight CG4684 travelling from Port Moresby to Kokoda today.
"We hold grave concerns for their safety and wellbeing," Mr Smith said.
Authorities believe they may have located a crash site and Australia is deploying a contingent of military assets to help with search efforts when they resume, weather permitting, at first light tomorrow.
Eight Australians were part of a Melbourne-based No Roads Expeditions tour group and another was an Australian tour guide.
Their families are being offered assistance by the Department of Foreign Affairs and Trade.
"This of course is an agonising time for these families," Mr Smith said.
There was also one Japanese national and three Papua New Guineans on board the plane.
The two crew members aboard are believed to be PNG pilots Jenny Moala and Royden Soauka.
An aviation industry insider said the missing plane had aborted its first landing attempt.
"We've heard she pulled out of the first attempt and a plane behind her landed, then she has done a loop and gone missing," they said.
The aircraft has an emergency locator beacon but no signal has been received.
Authorities were searching the Owen Stanley Ranges north of Port Moresby this evening but called it off after it got dark. They believe they might have narrowed the search area to a possible crash site.
"We hope, weather permitting, that a substantially-enhanced search and rescue effort can commence tomorrow morning," Mr Smith said.
Search and rescue efforts today - involving two helicopters and a twin-engine aircraft - were being hampered by bad weather, low visibility and very rugged terrain along the Kokoda Track.
"One of the helicopters has landed in a village which is thought to be near the vicinity of a possible crash site," Mr Smith said.
"I say a possible crash site because PNG authorities, PNG Airlines and Australian officials are relying on information relayed by villagers on the ground."
Mr Smith said Australia was working "single-mindedly" to help with locating the plane and those on board.
Late today, Mr Smith, Prime Minister Kevin Rudd, Defence Minister John Faulkner and Australian Defence Force chief Angus Houston met to discuss Australian efforts shortly after being informed the aircraft was missing.
Mr Rudd then spoke to Papua New Guinea Prime Minister Sir Michael Somare to offer assistance, which was accepted.
"Steps were taken to arrange the deployment of those assets," Mr Smith said.
HMAS Success, with a helicopter on board, is being diverted from near Torres Strait and will arrive off the PNG coast by first light tomorrow.
A Caribou aeroplane, currently in Port Moresby, will also be available to help. A C1-30 aircraft with medical facilities will depart overnight and be ready to assist.
"It will have on board a fully-equipped ground party with search and recovery assets," Mr Smith said.
Two Blackhawk helicopters will be deployed via a C-17 aircraft. The Australian Maritime Search and Rescue authority also deployed aircraft which left today.
The Australian High Commission in Port Moresby has established a consular crisis centre and was liaising with authorities.
People concerned about the welfare of family or friends are advised to contact DFAT's consular emergency centre on 02 6261 3305.