Parts of Victoria, NSW and Queensland have already topped 45C while the Northern Territory faces severe to extreme heatwave conditions for much of the next three days.
"It's very hot out there," Dean Narramore from the Bureau of Meteorology said on Monday.
Severe Weather Update: Extreme heat impacting south-east Australia today. Video current: 10am AEDT 16 December 2024.— Bureau of Meteorology, Australia (@BOM_au) For the latest forecasts and warnings, go to https://t.co/4W35o8iFmh or the BOM Weather app. pic.twitter.com/7AXauUyckjDecember 16, 2024
Multiple states have already topped 45C, with South Australia's Renmark and Queensland's Birdsville reaching 46C by Monday afternoon, while parts of northern Victoria and inland NSW had already reached 47C by 2pm.
Alice Springs in the NT is expected to reach up to 43C on Monday.
Extreme fire danger warnings are in place with high bushfire risks expected across Australia's southeast.
Mount Lofty Ranges in eastern South Australia and most of western and central Victoria, including Melbourne, are under extreme fire danger warnings.
"These hot, dry, windy conditions are likely to lead to extreme fire dangers," Mr Narramore said.
"That means that if fires do get going in this weather, they're likely to be uncontrollable and uncontainable."
With an expected high of 41C, Melbourne was on track for its hottest day since January 2023 and its hottest December day since 2019.
In Melbourne, those who could flocked to the beach to cool off. (Diego Fedele/AAP PHOTOS)
The mercury is expected to hit 46C in Mildura in the state's northwest, 45C in Swan Hill and 44C in Horsham.
Total fire bans have been declared across most of Victoria with incident management teams and firefighting aircraft on standby in critical regional areas.
Firefighters have already responded to blazes in western and eastern Victoria, and a grassfire in Melbourne.
A 'Leave Now' warning was issued for residents in Chetwynd in the state's west but was later downgraded as conditions eased.
While the mercury in Sydney reached 29C, parts of inland NSW have been hit with extreme heat.
A maximum temperature of 47C is expected in Wilcannia, in central northwest NSW, and 46.5C in Ivanhoe, about 180km further south.
A high fire danger warning was in place for much of central NSW on Tuesday.
Extreme fire danger has been declared in Victoria's central and western districts. (Con Chronis/AAP PHOTOS)
However, Queensland faces the risk of flash flooding with wet weather forecast from Yeppoon on the central coast south to Brisbane.
The bureau warned residents in the state's southeast to prepare for heavy falls in the coming days.
"Over the next three or four days, there could be widespread falls of 50mm to 100mm and isolated falls up to an exceeding 250mm," Mr Narromore told AAP.
Still, the extreme temperatures will likely be short-lived for NSW and Victoria, with heatwave conditions forecast to ease on Monday night.
A cool front had already reached Adelaide and western Victoria by 2pm on Monday, while Melburnians could expect some relief by 8pm or 9pm.
But the heat will remain for the rest of the week in Queensland and the NT.
36°C