Summer heat records have been smashed with South Australia's Port Augusta hitting a scorching 48.9C as the rest of the country sweltered though a heatwave.
The Bureau of Meteorology forecast daytime temperatures of up to 12C above average and 10C higher than usual at night from Monday to Friday.
All states and territories except Tasmania have centres where the temperature is due to stretch into the 40s.
At Port Augusta Tuesday's maximum was the highest since records began in 1962 with 47C forecast for Wednesday and Thursday ahead of a milder Friday.
The small town of Tarcoola in South the state's far north hit an eye-watering 49C on Tuesday.
"They are pretty incredible temperatures," senior forecaster Michael Efron said.
People in Adelaide didn't escape, with the SA capital reaching 41.2C.
The severe conditions in SA also took their toll on cyclists in the Tour Down Under with both the first and second stages shortened due to the heat.
Several towns along the NSW-Victoria border felt the hot weather with Mildura 46C.
In central NSW Ivanhoe got to 46.8C, while a sea breeze limited inner Sydney to 29C but the western suburbs including Penrith recorded 39.7C.
Australian Open players had cooler conditions than on Monday as Melbourne reached a bearable 30.4C, while outer suburbs like Scoresby reached 40.2C.
A total fire ban is in place across Victoria due to the risky conditions.
A widespread low-intensity heatwave is expected to stretch through to Friday from central Western Australia to southern parts of the Northern Territory and southwestern Queensland, as well as parts of Tasmania and Victoria.
Despite comparatively cooler temperatures, Tasmania is facing a severe bushfire threat, with low humidity and some 1200 dry lightning strikes.
Australian Associated Press