The number of animals which have died in Australia's bushfire season far has been revised up to more than one billion, "hastening extinction" for some species.

University of Sydney scientist Professor Chris Dickman has revised his estimate of the number of animals killed in bushfires in NSW to more than 800 million animals, with a national figure more than one billion animals.

Just weeks ago, Professor Dickman's estimate was 480 million animals, but with fires continuing and their range extending, the animals perishing in their path has become part of a "monstrous event" .

Toni Doherty saves a Koala injured in a bushfire near Long Flat in New South Wales. Photo / 9NEWS
Toni Doherty saves a Koala injured in a bushfire near Long Flat in New South Wales. Photo / 9NEWS

The University of Sydney reported that Professor Dickman has told National Public Radio in America that the bushfires and their devastation was unprecedented.

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"I think there's nothing quite to compare with the devastation that's going on over such a large area so quickly," he said.

"It's a monstrous event in terms of geography and the number of individual animals affected."

"We know that Australian biodiversity has been going down over the last several decades, and it's probably fairly well known that Australia's got the world's highest rate of extinction for mammals.

"It's events like this that may well hasten the extinction process for a range of other species. So, it's a very sad time.

"We're probably looking at what climate change may look like for other parts of the world in the first stages in Australia at the moment."

The figures of animals dying in the fires includes mammals (excluding bats), birds and reptiles, but does not include frogs, insects or other invertebrates.

Mega-blaze forms as three fires merge


It's been a long night for firefighters in New South Wales, where three bush fires merged to create a massive blaze in the Snowy Mountains.

The 23,3000ha Green Valley fire merged with the nearby East Ournie Creek blaze and the 31,2000ha Dunns Road fire on Friday evening.

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Three fires have merged to form a
Three fires have merged to form a "mega-blaze" on the New South Wales and Victoria borders. Photo / News.com.au

NSW Premier Gladys Berejiklian said the extent of the damage wouldn't be known until later this morning.

The "mega-blaze" straddles the New South Wales and Victoria borders and covers more than 640,000ha.

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Firefighters warned a southerly change was moving rapidly across NSW and had caused some fires to spread quickly.

That change was not expected to reach some coastal areas until early this morning.

The NSW Rural Fire Service said the predicted southerly wind change did not eventuate across the Blue Mountains fire zone, which helped to ease fire activity.

The RFS added there were 147 bush and grass fires burning across NSW – 65 uncontained – as of 6am AEDT today.

A mega-blaze has formed at the Snowy Mountains on the border of NSW and Victoria. Photo / AP
A mega-blaze has formed at the Snowy Mountains on the border of NSW and Victoria. Photo / AP

Conditions have eased across most fire grounds, with only one fire at watch and act warning in place.

RFS crews will make the most of more favourable conditions to work on containing those fires.

In Victoria, strong winds of up to 100km/h sparked ember attacks on the communities of Swifts Creek and Omeo overnight.

Premier Daniel Andrews warned it was a "challenging time".

A bush fire emergency warning was in place for Davenport Village, Dinner Plain, Flourbag and Hotham Heights.

A watch and act warning was in place for a large area stretching east from Mallacoota, north past Burrowa-Pine Mountain and west past Dandongadale. The bush fire zone reaches as far as Orbost in the south.