Over 50 smaller blazes were burning out of control.
A sombre Scott Morrison said today defence personnel stand ready to assist firefighters, warning: "Sadly, we have lost two Australians and I fear that we will lose more before the day is out".
About 1,200 firefighters and 70 aircraft were deployed across a roughly 1,000-kilometre (620-mile) stretch of the seaboard.
"The school was lost, houses were burnt, people were burnt, lives were lost", said Sparks, who added that residents battled to save their houses and then had to walk out because their cars had blown.
Conditions helping the fires would worsen next week, the local authorities warned.
In Queensland, almost 50 wildfires were raging on Saturday.
The body of one of the victims was found in a burnt-out auto in Glen Innes.
A body was found in a burnt-out building near the east-coast town of Taree, police said, while another victim was found in a vehicle and a woman died despite medics trying for several hours to save her.
Ms Fletcher's body was discovered on Saturday night in a burnt-out home in the town of Johns River some 40km north of Taree on the mid-north coast.
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The fire service said in a Twitter article that fire action has eased across some fairgrounds but continues to pose a danger to homes. "We've got winds blowing, they're circling, it's like a cyclone".
"There are communities and fire grounds where we are expecting to tally up considerable losses of homes and other properties", Mr Fitzsimmons said. "We now have 31 out of 37 districts in Western Australia in the high fire rating, and three of those will go to catastrophic in the days ahead". The years 2018 and 2017 were Australia's third and fourth-hottest years.
The bureau's State of the Climate 2018 report said climate change had led to an increase in extreme heat events and increased the severity of other natural disasters, such as drought.
Oceans around Australia have warmed by around 1 °C since 1910, contributing to longer and more frequent marine heatwaves.
Even if global temperatures are contained to a 2C rise above pre-industrial levels - a limit set out in the landmark Paris accord, agreed by 188 nations in 2015 - scientists believe the country is facing a unsafe new normal.
The oceans around Australia are acidifying (the pH is decreasing).
Swathes of Australia have gone months without adequate rainfall, forcing farmers to truck in water at exorbitant cost, sell off livestock or leave their land to lay fallow.
Bushfires are frequent in Australia and an unlimited corps of fire-fighters had already been tackling sporadic blazes for months within the lead-up to the southern hemisphere summer time.
The fires, which are of unprecedented severity particularly this early in the season, come amid increasing divisions about climate change policy.