Areas of Adelaide and Sydney nudged 40C and some regional towns have smashed through that benchmark as much of the country's southeast is hit with searing heat.
The South Australian capital on Sunday notched up 39.6C while some suburbs topped 41C, similar to the scorching temperatures that many West Australians endured last week.
Hot air from central Australia also lifted temperatures across NSW, with Penrith and Richmond on the western fringes of Sydney hitting 39C.
While cooler at 31C, muggy conditions in Sydney's east made for an uncomfortable time.
Melburnians meanwhile fell just short of a predicted top of 38C.
The regional centres of Port Augusta in SA's west and Wilcannia in northwest NSW both exceeded 44C
A reprieve was due to arrive in the southeast late on Sunday, with southerly winds and below-average temperatures expected for Melbourne and Adelaide on Monday.
However, Sydney will endure another hot day with 33C expected in the east and 37C in the west
Parents have been warned to prevent their children getting sunburnt, with UV levels on Monday predicted to reach extreme levels.
Staff at the Women's and Children's Hospital in North Adelaide have treated 15 patients for severe sunburn in recent weeks.
Doctor Bernard Carney says parents and carers can't be too cautious about children being in the sun.
"It is incredibly distressing for children to be treated for sunburn. They are often in severe pain and require frequent dressing changes," he said.
"No parent wants to see their child suffer, especially from something that's preventable."
