A passenger plane carrying 13 people has been reported missing over Papua New Guinea.
The 20-seater Twin Otter craft disappeared at 10.53am (12.53am Irish time) after taking off from the capital Port Moresby.
The plane, which was carrying nine Australians, was en route to Kokoda, site of a hiking trail and famous World War II battle involving Australian troops.
The Australians were members of a Melbourne-based trekking group, No Roads Expeditions.
'These passengers include a tour group of eight Australians on their way to walk the Kokoda Track, as well as an Australian tour guide and one tour guide from Papua New Guinea,' No Roads told the AAP newswire.
PNG airline official Allen Tyson said search operations are being hampered by bad weather in the region.
Consular staff are said to be contacting families of the Australian passengers to offer consular assistance.
Australian Foreign Minister Stephen Smith stressed that officials in Port Moresby were doing everything they could to find the plane.
At least 19 planes have crashed since 2000 in Papua New Guinea, where rugged terrain and lack of internal connecting roads make air travel crucial for its 6m citizens.
Mr Smith said there had been no sign of the plane by nightfall, and a 'substantially enhanced search and rescue effort' would begin at first light with the assistance of half a dozen Australian army and maritime rescue aircraft.