The devastation from the Australia wildfires has reportedly wiped out a billion animals, leading to what one scientist describes as an “extinction crisis”.

Professor Chris Dickman told Metro that the fires mean the total dead could rise in the coming weeks and months, as temperatures in the country start to rise again.

Worse still, Prof Dickman, a leading ecologist from the University of Sydney, believes some species may be wiped out for good due to a lack of wet refuges.

He told the paper: “Some of the species which are of greatest concern already have small populations and restricted geographical distributions…

An injured koala rests in a washing basket at the Kangaroo Island Wildlife Park, on the edge of the fire zone (Getty)

Koalas sit inside a home in Cudlee Creek, South Australia, after being rescued from fires at a garden (AP)

“In previous fires that have been less intense, you can expect to find an area around a wetland patch or a swamp, but it’s not clear from what we’re seeing that those refuges will be found.

“We’re desperately hoping they will be. If they’re not it’s going to bad news for a whole range of species.”

Previous estimates of animals killed in the fires were in the range of half a billion, with 8,000 koalas wiped out in New South Wales alone - nearly a third of the total population in the region.

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More koalas – who eat leaves on highly flammable eucalyptus trees – are feared dead in other areas.

Recent video footage showed desperately thirsty koalas clinging to cyclists while being given water to drink, while kangaroos were seen fleeing terrifying walls of fire.

Harrowing images have also showed the cockatoos falling dead out of trees.

Lake Tahoe Basin Management Unit Capt. Dave Soldavini holds a baby kangaroo that was rescued from a wildfire, in Cobrunga, Australia (AP)

Kangaroos move as nearby property burn in a fire in Lithgow, New South Wales state (AP)

Residents in the path of wildfires razing southeast Australia have been urged to evacuate as hot and windy conditions are forecast to escalate the danger over the next two days.

The New South Wales Rural Fire Service (RFS) told fire-weary community meetings south of Sydney in the coastal towns of Nowra, Narooma and Batemans Bay that northwesterly winds were likely to once again drive blazes towards the coast.

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People on holiday have retreated to beaches and into the ocean in the area in recent weeks as destructive fires and choking smoke encroached on the tourist towns, scorching sand dunes in some places.

A large smoke plume is seen over a sheep property in the Parndana region in Kingscote, Australia (Getty)

A firefighter manages a controlled burn near Tomerong, Australia (AP)

This satellite image provided by NASA shows wildfires in Victoria and New South Wales (AP)

In the neighbouring state of Victoria, fire-threatened populations were also urged to act quickly on evacuation warnings.

"We can't guarantee your safety and we don't want to be putting emergency services - whether it be volunteers or paid staff - we do not want to put them in harm's way because people didn't follow advice that was given," Victoria Premier Daniel Andrews said.

The unprecedented fire crisis in southeast Australia has claimed at least 26 lives, destroyed more than 2,000 homes and shrouded major cities in smoke.

Prime Minister Scott Morrison has come under withering criticism both at home and abroad for downplaying the need for his government to address climate change, which experts say helps supercharge the blazes.

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