Penrith reached 48.9 degrees, the highest ever in Sydney, making it the hottest place on earth at the moment, while Canberra recorded the hottest ever temperature of 44 degrees.
Prime Minister Scott Morrison announced he would mobilize at least 3,000 members of the Defence Force Reserves to assist in bushfire efforts.
The compulsory call-out of the reservists is a first in the nation's history, Defence Minister Linda Reynolds said.
It comes as phone lines, internet and electricity have been cut off in many of the worst-hit coastal areas in the states of Victoria and New South Wales (NSW). 
Locals in the fire-struck areas have been posting photos and videos on social media showing the frightening conditions, with the bright summer day turning into darkness by 3 pm due to the thick smoke.
"#Fire Warning. Conditions deteriorating rapidly with numerous blazes now jumping to Emergency #Warning levels. The gusty forecast southerly is pushing north & will continue along the coast tonight. Smoke plumes are triggering storms," the weather bureau tweeted.
NSW Premier Gladys Berejiklian told reporters that the projected worsening conditions "are coming to fruition... I make no bones about that. We are in for a long night and we are yet to hit the worst of it."
"We are discouraging people from moving from where they are, given the serious threats and the fact that we have so many fires at an emergency level."
NSW has announced a statewide total fire ban for Sunday as well, with conditions expected to be severe in many parts of the state.
The fires have been a unceasing presence for weeks in Australia.
Victoria has declared a state of disaster for the first time in history, while New South Wales has declared a week-long state of emergency, the third one since November. 
In NSW, more than 148 fires are burning with 11 at emergency warning alert level, which means it is too late to leave the area and finding shelter is the only option for safety. While in Victoria there are more than 50 fires, with 13 at emergency level. 
Meanwhile, two people were killed in a "virtually unstoppable" bushfire in South Australia on Saturday. The prime minister said 23 people have died since September.
The two latest deaths occurred on Kangaroo Island, a popular tourist destination, where a fire has been burning since December 20, but saw "a very serious escalation" since Friday evening, South Australian premier Steven Marshall said. 
Up to 150,000 hectares have already been burnt on Australia's third-largest island, including tourist attractions and a visitor centre. 
Locals have posted footage of a so-called "fire twister" breaking out in the inferno that shows the intensity of the flames on the island. 
Tens of thousands of people have been evacuated from coastal towns in south-east Australia bracing for severe weather of heatwaves and strong winds. Fire authorities have said it is the largest peacetime evacuation in the country's history. 
In addition to calling up troops to tackle the fires, Morrison also announced that 20 million dollars (14 million US dollars) would be spent on leasing four additional water-bombing aircraft. He also said he will request additional support from overseas to battle the fires.
Morrison, who has come under verbal abuse by furious locals during a visit to blaze-affected areas, has cancelled official visits to India and Japan.
The Australian Navy continue to evacuate some 4,000 people trapped on Mallacoota beach in Victoria due to a fire that reached the edge of the township and blocked their exit. 
Six people are still missing in Victoria, the state premier said.
NSW Rural Fire Service Commissioner Shane Fitzsimmons said Saturday he feared that the Green Wattle Creek bushfire, about 80 kilometres south-east of Sydney, which has already burned more than 264,000 hectares, has the potential "for the fire to break out... and move into the western suburbs of Sydney." 
Bushfires have been raising havoc in all six of Australia's states and one territory since the bushfire season started early this year in September. Only the Australian Capital Territory has been spared so far.
More than 1,500 homes have been confirmed destroyed, while the total land area burned is now above 5 million hectares – an area larger than the Netherlands. 
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