Parts of Australia are forecast to reach temperatures as high as 48 degrees Celsius this weekend, as large parts of the north bake under some of the hottest temperatures in the world.
The Bureau of Meteorology is forecasting temperatures from northern Western Australia to Queensland to be between 4C and 10C above average over the next three days.
Among the hottest is a remote area just inland of Eighty Mile Beach in Western Australia's Pilbara region, which is forecast to reach up to 48C on Sunday, while Marble Bar is expected to reach 46C.
Senior forecaster Jonathan How said there were severe to extreme heatwave warnings in place across the entire north of the country, which would be a "shock to the system" for many in Queensland.
"We're not breaking any records at this stage, but it is still incredibly hot, incredibly uncomfortable for many people," he said.
"And for large parts of Queensland, it's been a really wet year so it can be a bit of a shock to the system as well, having this heat."
This is the first major heatwave that has occurred since emergency services in WA and NT switched to a bushfire-style warnings system for heatwaves including "watch and act" and "emergency" classifications.
The change in the warning system is a national approach, but other states and jurisdictions, including Queensland, will implement it on their own timeline.
While not under heatwave conditions, large parts of South Australia are also set to reach temperatures up to 10C above average on Saturday as hot air from WA's Pilbara feeds into the region.
Oodnadatta is forecast to reach 43C and Coober Pedy 42C, with catastrophic fire danger ratings forecast for the Lower Eyre Peninsula and Yorke Peninsula.
Marble Bar hottest in the world
It has already been a week of extreme heat for northern Australia.
On Wednesday Marble Bar, in Western Australia's Pilbara region, was the hottest place in the world reaching 46.2C, according to Mr How.
Several towns in south-east Queensland and northern New South Wales experienced temperatures not felt for several years.
It included Lismore which reached 36.9C on Tuesday, its highest temperature since last December
"And quite a few other locations around the Northern Territory and Queensland also made it into the top 20 [in the world] as well," Mr How said.
More than just maximum temperature considered
Heatwaves are defined as three or more days of unusually hot weather, relevant to the location and time of year.
Mr How said minimum temperatures often played a big role in a heatwave warning being issued.
"Overnight minimums mean our bodies aren't able to cool down, and that can lead to heat stress, especially for elderly and vulnerable people as well," he said.
He said said heatwave conditions could be especially dangerous following a cooler period, which eastern Australia had been experiencing.
According to the bureau, the vulnerability of people in certain conditions also helps guide the classification, including how acclimatised people are to the heat and how well the infrastructure would cope.
For many Marble Bar locals, however, the heat is a part of the lifestyle.
Pam Townsend, who moved to town three months ago but has lived in other hot Australian towns, said she could deal with the 45C days.
"The reality is, most of us come to work in air-conditioning, drive our air-conditioned cars, and go home to our air-conditioned houses," she said.
"People just don't get around in the heat. They do the smart and sensible thing — stay indoors and don't, you know, get out and get in the hot sun, and they keep hydrated."
What is triggering the heat?
Mr How said the hot conditions had been fuelled by a lack of "cooling" features over the north, like rainfall, combined with the position of the sun this time of year.
"We are also seeing this weakening off of the negative Indian Ocean Dipole," he said.
"Just this week we declared it back to neutral which does mean we're getting less cloud across northern Australia."
He said the extremely warm ocean conditions had also been weakening the sea breeze.
"Especially around the Gulf of Carpentaria and the Coral Sea, they've had their warmest sea surface temperatures for spring on record," he said.
"So that means that any kind of sea breeze that comes through will be generally weaker than what you'd expect."
Heatwave conditions are expected to break up into next week, with some rain returning to northern Australia.
