Devastating blazes raging across eastern Australia is a taste of "extreme fire" predicted to become more frequent here under climate change, experts say.

More than 60 fires have been tearing through New South Wales and Queensland over past days, killing three people, razing 200 buildings, and forcing NSW Premier to declare a state of emergency as conditions only worsen.

The stage had been set years ago: a long stretch of drought, as well as a series of heatwaves in the past 12 months, had baked eastern Australia's landscape brown and primed it to burn.

Grasses had been reduced to dead, dry brown stalks, while nearly all of the vegetation in forests – from large branches and logs to twigs and organic matter on the ground – had become available to burn.

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Australia's iconic and widespread eucalyptus tree also happened to be one of the most flammable tree species in the world, Scion fire scientist Grant Pearce explained.

When released, the pleasant-smelling oils within the trees pushed up the flammability of surrounding foliage and air – and their strips of bark provided a source of long-burning embers.

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All of that could result in what were called mass ember storms which, when carried to great heights by the fires' towering convection columns, triggered new fires kilometres downwind.

Pearce said these massive fires even drove their own weather by interacting the upper atmosphere, stirring convection columns that could form thunderstorms and spark yet more fires with lightning.

"Suppression of such fires is difficult if not impossible, due to the high fire intensities and erratic fire spread," he said.

"Any water or retardants, made even more scarce by the drought conditions, is quickly evaporated by the intense heat before it can wet the vegetation - whether applied through hoses or aircraft, or even large water-bombers dropping tens of thousands of litres at a time."

He expected the big flames would be burning at around 1300C and spreading at rates of up to 12km an hour.

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That made it too unsafe to put firefighters on the ground ahead of the fires – so they instead had to tackle them from the backs and sides, or through making firebreaks well ahead of the burning area.

Fire seen from Forster, New South Wales. Photo / Supplied
Fire seen from Forster, New South Wales. Photo / Supplied

Pearce said some Australian fire managers had described the current fires as unprecedented, in terms of their conditions, how early in the season they'd started, and the scale and ferocity with which multiple fires were now burning.

"This is despite both NSW and Queensland having a long history of extreme fire events.

"However, the frequency of such incidents, and of severe fire seasons generally, has increased in recent years."

Research had shown that fire risk in New Zealand would also likely increase under climate change, with a greater frequency of severe fire weather days in many parts of the country - in some cases by two to three times current levels.

"Fire seasons are also getting longer, both starting earlier and extending longer into autumn," Pearce said.

That meant the potential for not only more fires, but larger and extreme ones, like the big blaze that tore across 35km of Nelson's Pigeon Valley in February.

"More fires also mean more wildfire smoke, with greater potential health impacts for vulnerable people, including people with respiratory conditions, and the very young and elderly."

Meanwhile, meteorologists say more plumes of dust from the Australia fires are expected to cross the Tasman Sea this week.

This satellite image, taken from the NASA Earth Observatory, shows the extent of fires burning across eastern Australia. Photo / NASA
This satellite image, taken from the NASA Earth Observatory, shows the extent of fires burning across eastern Australia. Photo / NASA

Niwa forecaster Ben Noll said the next plume was due into New Zealand late Wednesday or Wednesday night, potentially reaching across the North Island.

"There were some reports of dust covering vehicles in the South Island over the weekend—so maybe a car wash will be required."