No deaths or serious injuries were reported as of Monday morning, but the bushfires have caused extensive damage in rural areas of Victoria and New South Wales (NSW). At least 75 homes had been destroyed, authorities said, Reuters reported.
"We can't be 100 percent sure that everybody is accounted for... but each one of those homes that have been affected by fire will need to be looked at and just confirm that," NSW Rural Fire Service Deputy Commissioner Rob Rogers told Australian Broadcasting Corp.
"There are 22 fires and five of those are not contained. There's still a lot of fire around the landscape," he said, adding it would be at least several days before they were extinguished.
The fires, believed to have been sparked by lightning on Saturday, were fanned by dry, hot winds as temperatures reached 41 C (106 F) throughout Sunday.
Emergency officials said conditions should ease on Monday but "watch and act" warnings remained in place for five locations.
At least 70 homes and a school were destroyed in the small coastal town of Tathra in New South Wales, authorities said, where people fled to the beach to avoid the flames and flying embers carried the fire front forward quickly.
About 700 residents were evacuated to centers set up at the nearby town of Bega and several schools in affected areas were closed on Monday.
About 280 firefighters were battling the blazes while 22,000 homes were without power in the region after the high winds brought down trees, Emergency Management Commissioner Craig Lapsley said late on Sunday.
In the north Australian city of Darwin, about 25,000 homes were also without power after a tropical cyclone felled trees. No deaths were reported.
Bushfires are a common and deadly threat in Australia's hot, dry summers, fueled by highly flammable eucalyptus trees.
In January, hundreds of holidaymakers had to be evacuated by boat from the beaches of the Royal National Park south of Sydney, when they became trapped by bushfires.
The 2009 Black Saturday bushfires in Victoria killed 173 people and injured more than 400.