These rural towns are all about to endure four days above 40 degrees. Birdsville in Queensland and Moomba in South Australia will suffer through three days above 45, with Birdsville not having had a day below 43 degrees since Australia Day.

This summer's most extensive, and brutal, heatwave is building over central and eastern Australia.

Inland parts of Queensland, New South Wales, South Australia and northern Victoria are set to swelter through at least four days of extreme heat, according to the Bureau of Meteorology.

Meteorologist Andrea Pearce said "pools" of hot air had been hovering over the centre of Australia, leading to the build up of heat.

"We've had a high pressure system sitting across southern Queensland and northern New South Wales for weeks now, and it's been preventing any frontal systems coming through and flushing out all of that really hot air," she said.

"We've had over 40 degrees in many, many locations and we expect that to continue. We see a relentless pool of temperatures above 40 degrees."

The only cool place to escape the heat? The pub, according to Birdsville Hotel manager Ben Fullagar.

"We've got the coolest building in town, it's fully air-conditioned, a stone building," he explained.

"All we can hope is that the air-conditioners and refrigerators don't pack it in, because they can only take so much."

On Sunday, however, a new weather front will start to move through Australia, dropping the mercury in most of Victoria and South Australia.

By Monday, New South Wales should begin to feel the cool change, followed by Queensland.

VICTORIA

Northern parts of the state are in for the hottest conditions, with Mildura expected to get two days of 44 degrees on Thursday and Friday, dropping to 42 degrees on Saturday.

Echuca, on the border of NSW, is expected to cop 41 degrees on Thursday, 43 degrees Friday and 40 degrees on Saturday.

"In Victoria the winds have turned northerly, so some of that very hot air is going to move across Victoria, especially in the north of the state," Bureau of Meteorology forecaster Chris Godfred said.

"We're going to see temperatures rise well above 40, and then that heat will continue across until the weekend, and we'll get a cool change on Sunday."

The hot air will move to Albury on Friday, where temperatures will reach 43 degrees, and then 41 degrees on Saturday.

Melbourne will be cooler, with a top of 37 degrees on Thursday, dropping to 26 degrees on Friday.

Melburnians might survive summer without recording a single 40-degree day.

NEW SOUTH WALES

Wet weather in Sydney has made way for warmer conditions as the interior heat leaks eastwards.

Bourke, a small town 800 kilometres north-west of Sydney, is expected to record Australia's hottest temperature for the week, peaking at 47 degrees on Sunday.

In Penrith, Thursday's forecast top of 36 degrees will seem almost cool given what's expected after that. Friday to Sunday, the mercury is expected to climb to 44-45 degrees.

A top of 29 degrees is predicted for Sydney on Thursday before a trio of scorching days, with 36, 39, and 38 degrees forecast by the Bureau of Meteorology for Friday through to Sunday.

Weatherzone meteorologist Graeme Brittain said it could be the hottest three-day spell on record for Sydneysiders.

The hottest towns in Australia this week. Photo: Bureau of Meteorology

QUEENSLAND

Birdsville, a town of only 120, has sweltered through temperatures above 43 degrees since Australia Day.

"We've had hotter days, it's just difficult at the moment because it's day after day – normally we get a break, but not this year," Birdsville Hotel manager Ben Fullagar said.

"But life will just continue on the same track here in Birdsville."

Inland centres such as Ipswich and Gatton are also forecast to reach some of the hottest temperatures recorded for the region, particularly over the weekend.

"We're expecting temperatures to reach the high 30s for Saturday and reach over 40 degrees on Sunday, with Gatton expecting 42 and Ipswich 41," Bureau senior forecaster Brett Harrison said.

Brisbane temperatures will be in the low 30s over the next few days, but the city is forecast to hit 35 on Saturday and 37 degrees on Sunday.

SOUTH AUSTRALIA

In Moomba, an outback town 770 kilometres north of Adelaide, a new record could be set for the most days about 45 degrees.

The Bureau of Meteorology predicts the town is in for a six-day stretch above 45 degrees, dropping to a "mild" 39 on Sunday.

An extreme heat warning was issued by the Bureau for the state on Wednesday.

Adelaide reached 42.4 degrees on Wednesday, and will get to 41 degrees Thursday. Friday and Saturday temperatures will remain high, above 37 degrees.

South Australia was hit by a short power outage late on Wednesday as searing heat led to a spike in electricity use, just months after a major blackout hit industry and forced a review of energy security in the renewables-dependent state.

Load-shedding, which began Wednesday evening, lasted for about half an hour and affected around 40,000 people, the country's electricity market operator said, adding that it would investigate the issue.

The state, which is heavily dependent on wind and solar energy, was crippled by several outages late last year, after heavy winds knocked out an interstate power connector and cut power to residents and industry.

- with Reuters