Victorians are set to swelter through heatwave conditions with temperatures to soar into the 40s this long weekend.
Bureau of Meteorology senior meteorologist Christie Johnson said northern parts of the state could see temperatures into the 40s for potentially five or six days in a row.
Fire crews are on alert with seven outbreaks still burning, including three that are out of control.
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Johnson said Tuesday could be a day of concern with near record temperatures about 48 degrees.
"It could definitely be one of the hottest days that we've ever seen over Victoria," she said.
Water police will be out in force with hundreds expected to pack beaches across the coast over the long weekend.
Residents have been warned to take care as the blistering sun can be deadly.
"People becoming dehydrated and leading to heat stress and stroke, but it can exacerbate normal medical problems as well, which increases our workload," Ambulance Victoria's Andrew Burns said.
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South Australia on track for record-breaking heat
South Australia is also on the verge of an unprecedented heatwave with soaring temperatures expected over the next three days combined with catastrophic fire danger keeping authorities on high alert.
"Make no mistake, the state is set to bake for much of the next week," the Bureau of Meteorology's John Fisher said.
Today's forecast is expected to reach 43 degrees with conditions creating catastrophic fire danger for the Yorke Peninsula and the eastern Eyre Peninsula.
"I urge people to take [Saturday] seriously," Country Fire Authority chief officer Brett Loughlin said.
"The risk of fires spreading quickly and uncontrollably across the landscape is real.
"If major fires develop [Saturday], they will test our firefighting capabilities, and put our people on the front line of a major challenging scenario."
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Emergency Services Minister Rhiannon Pearce said additional aircraft, including a large aerial tanker, would be deployed if required.
The mercury is predicted to reach 45 degrees just two days later, potentially setting the stage for Adelaide's hottest Australia Day on record and the highest temperature the city has seen since December 2019, when deadly fires ripped through scrub at Cudlee Creek.
Those planning long weekend road trips have been asked to think twice.
"Don't go into the highest risk fire areas, and if you are and you have accommodation booked, please be sensible about it," Loughlin said.
City celebrations have also been affected, the Australia Day Council pushing the start of its Elder Park program back to 7pm.
"We have misting stations, plenty of water available and extra shade," Australia Day spokesperson Gwen Gaff said.
High electricity demand could also cause significant strain, making power outages a possibility.
"Common sense - we can do this, we can get through this hot weather if we work together and we make sensible decisions," Loughlin said.
Queensland braces for storms
Queensland is bracing for wild weather of a different kind as a tropical low builds off the state's north-west.
Tropical low 18U was tonight in the eastern Gulf of Carpentaria and had a moderate chance of developing into a tropical cyclone over the weekend.
Residents of North Queensland and eastern Northern Territory have been warned to monitor for updates.
Another low lies in the Coral Sea off Queensland's north-west coast but is unlikely to become a tropical cyclone and is expected to remain offshore.
Flood warnings are also in place in parts of the state, which experienced destructive flooding just weeks ago.
Moderate flood warnings have been issued for Bedourie and Windorah from Sunday and Glengyle from early next week.
A minor flood warning is in effect for the Sutton River.
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