This handout photo released by the Royal Australian Navy shows people being evacuated from Mallacoota. AFP

A dangerous fire flared up in southeastern Australia on Sunday even as cooler conditions elsewhere allowed authorities to begin assessing the damage from heatwave-spurred blazes that swept through two states on Saturday.

Officials told residents and others in the New South Wales (NSW) state town of Eden to leave immediately and head north if they did not have a bushfire response plan.

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Australia orders evacuation of fire-ravaged towns before heatwave

"If your plan is to leave, or you are not prepared, leave towards Merimbula or Pambula," the Rural Fire Service said in an alert.

Tens of thousands of homes in both NSW and Victoria states were without power on Sunday as a large-scale military and police effort continued to provide supplies and evacuate thousands of people who have been trapped for days in coastal towns by the fires.

The haze from bushfires obscures the sun setting above the Sydney Opera House in Sydney, Australia. File photo/Reuters

Initial estimates put damaged or destroyed properties in the hundreds, but authorities said the mass evacuations by residents of at-risk areas appear to have prevented major loss of life. Twenty-four people have been killed since the start of this year's wildfire season.

Sunday's cooler temperatures and light rain forecast in some coastal areas in coming days could bring some relief, but officials said that would not be enough to bring the almost 200 fires still burning under control.

A view of a property impacted by the Currowan Fire in Conjola Park, Australia, on Thursday. Heather Mcnab/Reuters

Fire officials said the next major flashpoint would come later in the week, but it was too early to gauge the likely severity of the threat.

"The weather activity we're seeing, the extent and spread of the fires, the speed at which they're going, the way in which they are attacking communities who have never ever seen fire before is unprecedented," NSW Premier Gladys Berejiklian said.

Thousands of people have been evacuated from coastal towns at the peak of the summer holiday season, in one of the biggest coordinated operations since the evacuation of Darwin after Cyclone Tracy flattened the northern city in 1974.

Australia has been battling blazes across much of its east coast for months, with experts saying climate change has been a major factor in a three-year drought that has left much of the country's bushland tinder-dry and susceptible to fires.