Large parts of NSW and Queensland are set to swelter through Friday and the weekend as the first heatwave of summer gets set to hit the east coast and last until mid next week.
In Sydney, temperatures in the city's west are set to climb to 37 degrees, the Bureau of Meteorology forecasts. In Sydney city, the temperature is tipped to reach a less stuffy 31C, thanks to a sea breeze, with a possible afternoon thunderstorm.
A total fire ban has been declared for Sydney, while much of the rest of the state is under high or very high fire danger. The only regions considered at low to moderate fire danger are Northern and Southern Riverina and South Western.
Meanwhile, health authorities are urging Queenslanders to look after themselves over the next few days, as the mercury soars into the high 30s.
Brisbane is forecast to reach 32C on Friday, but temperatures are predicted to reach 37C in Ipswich and even higher in places like Gatton and Birdsville where the mercury is likely to reach the 40s.
For Saturday, BoM has revised down its initial prediction of 38C for Brisbane tomorrow, which would have been the city's hottest December day since 2001, according to the Nine Network.
Senior BOM forecaster Rick Threlfall said NSW and Queensland could expect a prolonged period of hot and humid temperatures until next Wednesday.
"The length of it is the main factor," he told the Nine Network. "Often we'll get three or four days of it but the fact that its going on for close to a week is what makes it unusual."
The hot weather in Queensland comes after dramatic storms lashed parts of the state's southeast overnight.