Emergency services are bracing for scorching conditions across South Australia and Victoria, with an expert warning that "nowhere is going to escape the heat" as sweltering temperatures threaten to break all-time records.
In South Australia, Ceduna reached its hottest day on record on Wednesday with the mercury climbing to 48.4 degrees Celsius just before 3:00pm — half-a-degree hotter than the record set in 1990.
"South Australia is once again experiencing a severe heatwave," said Jonathan Fischer, a Bureau of Meteorology emergency services meteorologist.
"Nowhere is going to escape the heat [today]."
Mr Fischer said temperatures had peaked in the mid-to-high 40s across the north and west of SA on Wednesday and a northerly wind change today will mean the whole state will feel the heat.
"It's fair to say we will see records broken … with many locations forecast to be near their maximum all-time record," he said.
Across SA, Port Pirie reached 45.2C just after 5:00pm on Wednesday, while Port Augusta reached 45C.
Roxby Downs was also among the hottest with a peak of 46.5C while in the Adelaide CBD the peak temperature was 40.9C.
The heatwave has prompted fire bans across 13 districts in South Australia today, with expected winds making for dangerous conditions.
"If a fire does start with these forecast weather conditions we're not going to be able to control that fire," said Yvette Dowling, Country Fire Service SA state duty commander.
"The communities are at risk, our firefighters are at risk, all emergency services are at risk."
Fires still burning across Victoria
In Victoria, emergency management commissioner Andrew Crisp said there had been 66 fires across the state in the last 24 hours and dangerous conditions will peak on Friday, when a total fire ban for Victoria will be declared.
Three blazes in far-east Gippsland are still raging, with one at Timbarra burning through 400 hectares.
"I urge everyone to download the Vic Emergency app and if you're travelling, know who the emergency broadcaster is," he said.
Commissioner Crisp said he was aware a unit at the Loy Yang power station was down but it was expected to be back online Saturday and "at this stage I've got no advice that there's no sufficient [electricity] reserve at this point in time".
Richard Russell from the BOM said temperatures were going to be "nothing short of oppressive", particularly in northern Victoria where the mercury is expected to reach up to the mid-40s today.
"We'll see those conditions spread across most of the state for Friday [with] incredibly high minimum temperatures on Thursday night … in Melbourne we expect the minimum temperature to only get down to 29C, much of the state will barely dip below 30C during that period," he said.
"Melbourne's all-time overnight record is 30.6C, so it's getting pretty close."
Temperatures on Friday in the north-east could push above 45C, with strengthening northerly winds causing severe to extreme fire dangers across the state.
Ambulance Victoria has issued heat health alerts across most of Victoria for today and is urging people to take steps to stay cool and check on elderly or vulnerable people.
Since December 1, paramedics have been called to over 300 incidents with kids locked in cars.
A strong change is forecast during Friday, reaching Melbourne around 4:00pm.
All-time records to be tested
Mr Fischer said the record temperature for Adelaide was expected to be pushed today, with a forecast temperature of 45C expected.
"For the eastern and northern suburbs it's likely to be a little bit hotter than that, 46 degrees, so close to the all-time record for Adelaide which is 46.1 degrees back in 1939," he said.
Port Augusta has been tipped to reach temperatures of 49C, while Port Pirie has also been tipped to reach 47C.
Robe is the only SA town expected to reach a maximum temperature under 40C, with a forecast of 37C.
A cool change is expected to move across South Australia on Friday and into the weekend.
In Victoria, temperatures are expected to reach the mid-40s in Mildura and low-40s in Horsham across today and tomorrow.
A top of 46C is currently forecast for Mildura tomorrow.
Alfred Mason, Country Fire Authority District 17 acting operations manager, said strong winds for the Mallee and Wimmera regions tomorrow would make for dangerous fire conditions.
"We are looking in the Mallee at north-westerly winds up to 40 kilometres an hour on Friday," he said.
"The bush is extremely dry but on a warm Wimmera and Mallee day, if the winds are there, that's what is going to create the fire for us. The higher the wind speed, the higher the fire rating."ABC