"It's rare on earth in this century," Australian wildlife ecologist and report author Barry Traill told local radio. "We need to hold onto this country. It's just so precious," he said.

Australia was one of five great remaining wilderness zones, along with Antarctica, the Amazon, the Sahara Desert and Canada's northern Boreal, the report said.

Most of the untouched areas were in the country's vast interior and northern savanna, including largely Aboriginal Arnhem Land, northern Cape York Peninsula, the vast southwest Nullarbor plain and the central Gibson desert.

Pristine areas faced their biggest threat from introduced feral animal and plant species including pigs, rabbits, foxes, buffaloes and noxious weeds, the report said.

"Around that core of wild lands, hundreds of millions more acres are healthy enough that they can still support the maintenance of resilient ecosystems," Pew said on its website.

In addition to its wilderness treasures, Australia had some of the world's most protected marine areas, with the Great Barrier Reef the largest living organism, it said.

Australia, the world's oldest continent, ranked first globally for the total number of unique native mammal and reptile species, and among the top five countries in total numbers of endemic plants, birds and amphibians.

Traill said Australia's government should be recruiting up to 5,000 extra Aboriginal rangers to act as guardians of untouched areas, with only 10 percent of the country currently protected as parklands and reserve.

"If you drive through and see these vast areas of bushland, it looks in pretty good shape, but there are subtle changes happening, and we need to get people back out there managing it," he said. (Editing by David Fogarty)