A burst of extreme summer heat in southern and eastern Australia, including Adelaide and Melbourne, has been dragged down from Western Australia's Pilbara region, which has experienced record-breaking temperatures in the past fortnight.

Key points: The Pilbara has a dry, desert-like climate perfect for generating heat

The Pilbara has a dry, desert-like climate perfect for generating heat At this time of the year the sun is perfectly positioned to deliver solar radiation

At this time of the year the sun is perfectly positioned to deliver solar radiation Prevailing north-westerly winds carry this heat to Victoria and South Australia

Intense heat has been building in the Pilbara, with temperatures in some towns hovering in the mid to high 40s over the past two weeks.

Marble Bar recorded 49.3 degrees Celsius on December 27 — the hottest day in the town since temperature records began in 1901.

The heat is now spreading to the south-east of the country with parts of Adelaide reaching above 42C on Thursday, while the South Australian town of Ceduna soared to 47.1C.

Heatwaves generated in the Pilbara have extended across the country this summer. ( Supplied: BOM )

Today, the blistering heat will affect Victoria, Tasmania, the ACT and southern parts of New South Wales.

Maximum temperatures in Victoria will be 10 to 16 degrees above average, with Melbourne tipped to reach 42C — a temperature the city experiences once every three to five years.

The movement of hot air from north-western to south-eastern parts of Australia is typical of Australian summers.

The perfect conditions to brew a heatwave

Bureau of Meteorology climatologist Glenn Cook said the Pilbara generated blistering hot conditions due to its dry, desert-like climate and the position of the sun during the summer months.

"The Pilbara is a prime area for high temperatures because of the sun's elevation at this time of year, so the angle of the sun above the horizon — it's pretty much directly overhead at this time of year — so it gets the maximum amount of solar radiation that you can get anywhere in Australia really," he said.

The high temperatures are expected to continue in the Pilbara with no relief in sight. ( Pixabay: Dimitris Vetsikas )

"Also because it is a relatively dry climate and has pretty sparse vegetation, that means the landscape can absorb huge amounts of solar radiation from the sun and heat up quite significantly."

Mr Cook said the recent lack of rainfall over the region had contributed to the heat.

"We have not had any sort of monsoon burst over the Pilbara up to this point in the wet season.

"Typically, we can get tropical lows or tropical cyclones through the region in December or early January so they will reduce the heat."

So how does Pilbara heat get to Melbourne?

The one saving grace for Melbourne is that the extreme heat will be short-lived —a cooler weekend is forecast. ( AAP: David Crosling )

In Australia, weather systems such as troughs move from the west to the east, which is why the hot air mass from the Pilbara is funnelling down to the other side of Australia.

"Typically in summertime we have low-pressure troughs that move from the west to the east of the country and ahead of those troughs we tend to get north-westerly winds that bring the air from the north-west down to the south-east," Mr Cook said.

"So that prime region of heat up in the Pilbara is set up to be dragged down ahead of a trough as it moves down to the south-east over southern parts of the Northern Territory, South Australia, New South Wales and Victoria."

The good news is that there will be a rapid cool change over the south-east with Melbourne's temperature set to drop by about 20C on Saturday.

But the same cannot be said for the Pilbara, which is in the midst of a static weather pattern.

"They need a big high-pressure system to move in and push some southerly winds up there to move that heat away, but that's not really happening and it's not forecast to happen at least over the next week," Mr Cook said.