Regional Australia bore the brunt of Thursday's heatwave, with temperatures in some parts of the country just shy of a 53-year record.
Moomba in the far north of South Australia baked with 49.3C, not much short of the hottest temperature ever recorded in Australia, 50.7C in Oodnadatta on this day in 1960.
Western and northern parts of Queensland endured searing heat, with some 20 towns recording temperatures above 40C on Thursday.
The highest was in Birdsville where it reached 48.7C at 4.39pm, not far off its 49.5C record.
Some of the sunshine state's heat crossed into NSW, with hinterland towns near the Queensland border sweltering, the Bureau of Meteorology said.
"It's just gone up to 48.4 at Tibooburra, so it may climb in the next couple of hours, but I don't think it will break 49," Bureau forecaster Olenka Duma told AAP at 5pm (AEDT).
Bourke residents faced a high of 46.8C.
"It's still going to be hot tomorrow up in that area," Ms Duma said.
"Saturday is when the temperatures will start to see a good 10 to 15-degree drop."
There will be little relief in Queensland, with Brisbane set to endure one of its hottest ever days with a rare 41C on Saturday.
Those living on the SA coast beat NSW to a cool change, with Kuitpo Forest, in the Adelaide Hills, just 14.5C and Parndana on Kangaroo Island had 15.7C.
The weather bureau forecast conditions to moderate across the north of SA on Friday, with temperatures to fall to the mid to low 30s in most places.
However, Moomba was expected to hit 40C before a drop to 32C on Saturday.
Temperatures hit 45 degrees in Queensland regional towns Camooweal and Century Mine.
Queensland, SA and NSW have issued severe and extreme fire warnings for parts of each state on Friday.
SA's south will remain cool to mild however, with Adelaide tipped to have a top temperature of 23C.
In inner Sydney a cool change swept through mid-afternoon, bringing the mercury at Observatory Hill down from 34.5C at 3pm to 23.7C by Thursday evening.
In Central Australia temperatures reached 42.9C by 9.30am on Thursday, with Tennant Creek recording its hottest-ever January day at 45.1C.
Denise Broad, who lives north of Alice Springs on the Plenty Highway, told AAP the heatwave of 40C-plus temperatures since Saturday was the longest she could remember since moving to the station almost 34 years ago.
BoM senior forecaster Mark Kersemakers said no rain was on the horizon for the region, but a cool change was forecast for the weekend.
In WA, outback towns Fitzroy Crossing was tipped to hit 42C, while Argyle and Kununurra are expected to hit 41C.
Tasmania and Victoria escaped the heat altogether.
