Australia has narrowly missed out on making it three in a row for its hottest-ever days, but other temperature records have still been tumbling by big margins.

Bureau of Meteorology data suggests the national average maximum temperature reached 41.0 degrees Celsius on Thursday, after hitting 41.9C on Wednesday and 40.7C on Tuesday.

Before this week, the record of 40.3C had stood since January 2013.

But Victoria's December record for an individual location was smashed today when it reached 47.9C at Hopetoun Airport and Horsham, well above the old mark of 46.6C set in 1976.

The ongoing heat saw the national location record for December broken twice within the space of a few hours on Thursday — Eucla in Western Australia reached 49.8C before it was eclipsed by SA's Nullarbor weather station with 49.9C.

The old record had been set at Birdsville (49.5C) in 1972.

Adelaide (45.3C) and Canberra (39.3C) also broke December record temperatures on Thursday that had stood since 1994.

The SA capital suffered through its hottest December night on record, one of the deadliest parts of a heatwave — hot nights mean the body doesn't have a chance to cool down and recover.

Yes, climate change is involved

The records this week have not just been broken, they have been surpassed by big margins.

Professor David Karoly, a leading climate scientist at the CSIRO, said the cause was clear.

"We're smashing the extremes by effectively a degree relative to the other cases because that's by how much the Australian temperatures have warmed," he said.

Before this week the 10 hottest days on record were within 0.25C — the average maximum reached on Wednesday broke the hottest day prior to this event by 1.6C.

A range of natural phenomena were pushing temperatures up, Professor Karoly said, but on top of that was a trend driven by greenhouse gasses in the atmosphere.

"Climate change has contributed between 1C and 1.5C on top of the natural variability," he said.

Dr Sophie Lewis, a climate scientist at the University of New South Wales, said these records were "exceptional".

"It's not just the frequency that we're breaking them, it's the margin," she said.

Without climate change, she said, Australia would probably never have seen events like this.

"We're now seeing temperatures that are occurring outside what we'd expect from natural variability alone.

"We'll definitely have to crunch the numbers on this week, but there are certainly cases where we've seen temperatures that are so extreme, that they are not what we'd expect without that additional kick from climate change."

Then there is the fire

This is the fourth day of extreme heatwave conditions for large parts of South Australia, where fires have raged throughout the day.

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Meanwhile, the horror fire season continues in New South Wales, where two firefighters died on Thursday and the number of homes lost this year is more than 800.

Smoke from the NSW blazes has also made it all the way to Melbourne, as hot northerly winds drive up the temperatures across the state.

Saturday is expected to bring more hot conditions to New South Wales, where catastrophic fire conditions are forecast.

The fires are already the most widespread the state's east coast has seen in modern memory.

When is the change?

A cool change is already on its way through, but will generate horror fire conditions before it delivers a drop in temperatures.

After making its way across South Australia overnight Friday, the change is forecast to move over NSW, bringing another peak in fire conditions before things cool off moving into next week.