The river-dwelling animal has already disappeared from up to 40 percent of its historical range on Australia's east coast due to the drought, land clearing, pollution and building of dams, which fragment their habitat, the researchers said.

They predicted that if the current threats persist, platypus numbers will fall another 47-66 percent over the next 50 years.

If projections about worsening climate change are taken into account, the numbers of the duck-billed, egg-laying mammal could plummet up to 73 percent by 2070, they wrote.

The platypus is listed as "near threatened" by the International Union for Conservation of Nature.

But the scientists from the University of New South Wales' Centre for Ecosystem Science said damage to river systems caused by years of little rainfall and high temperatures had worsened prospects for the animal.

"These dangers further expose the platypus to even worse local extinctions, with no capacity to repopulate areas," said Gilad Bino, lead author of the study.

The scientists said there is an "urgent need" for a national risk assessment to determine if the platypus should be downgraded to "vulnerable" status and to lay out conservation steps "to minimise any risk of extinction".

The study is the first across all platypus habitat zones to establish a so-called "metapopulation" model while also projecting the impacts of climate change on the species going forward.

The survey estimated the total platypus population had fallen by 50 percent since European settlement of the continent two centuries ago.

An earlier study published in November 2018 estimated the population had fallen by 30 percent over that period, to around 200,000.

"Under predicted climate change, the losses forecast were far greater because of increases in extreme drought frequencies and duration, such as the current dry spell," Bino said of the latest report.

The new study comes as unprecedented bushfires ravage vast areas of eastern Australia, fuelled by the drought and record-high temperatures.

The platypus, which along with four species of echidna are the only mammals that lay eggs, is one of the world's strangest animals, with the bill of a duck, tail of a beaver, otter-like feet and a venomous spur on its hind leg.