A major heatwave is still sweeping across the nation's southeast, with temperatures reaching 43C in Melbourne and up to 47C in parts of inland Victoria and South Australia on Friday.
Damaging northwesterly winds of up to 90km/h are combining with extreme heat to break temperature records and bring catastrophic bushfire conditions, the Bureau of Meteorology says.
"We have severe heatwave warnings current for all states and territories except Queensland," senior bureau meteorologist Christie Johnson said on Friday.
"Some parts of Victoria and NSW are reaching extreme heatwave criteria."
The sweltering and gusty conditions in Victoria have fuelled massive bushfires in the northeast of the state with three people, including one child, unaccounted for in the Longwood fire 150km from Melbourne.
After bearing the brunt of the high temperatures on Thursday, the relieving cold front has passed through South Australia and into Victoria.
However, the front was not predicted to reach the Walwa fire district until Saturday morning, the bureau said.
While relief is on the way, authorities are warning the danger of severe weather will not disappear as the mercury drops.
The strong southwesterly wind change has prompted the bureau to issue severe weather warnings for damaging winds of up to 90km/h stretching from the South Australian interior to eastern Victoria.
The gusty conditions will also bring a risk of thunderstorms, including the chance of dry lightning igniting more fires.
"The change is forecast to reach Geelong and the Mornington Peninsula around 5-7pm and move through the Melbourne metro area between 6-8pm," Ms Johnson said.
Relief from the heat won't reach most of NSW until late Saturday or early Sunday, with much milder conditions expected in the succeeding days.
Before the cool change, the town of Wudinna on SA's Eyre Peninsula reached 48.2C on Thursday, just 0.2C shy of its record.
Regional centres of Renmark (47.2C), Whyalla (47.8C), and Port Augusta (47.6C) all recorded their hottest day in seven years.
The northwest Victorian towns of Walpeup and Hopetoun also recorded temperatures above 46C, their highest since 2019.
After recording 33C on Friday, things will likely worsen in Sydney on Saturday with temperatures expected to reach 42C and an even hotter forecast for the western suburbs.
A total fire ban for Saturday has been declared for the Greater Hunter, Sydney and extending all the way to the far south of the state.
NSW Ambulance chief superintendent Steve Vaughan urged residents to begin preparing for the hot conditions and to stay cool, hydrated, and indoors during the hottest part of the day.
"Heatwaves put real pressure on your body, with consecutive days of relentless heat causing stress that builds up over time," he said.
