The intense heat has so far been limited mostly to central western Australia but looks set to spread to other parts of the country, including South Australia, Victoria, New South Wales and Tasmania.
On Monday, one small town called Marble Bar – home to only 175 people in western Australia – registered more than 24 days straight with the mercury hitting at least 40C (104F), according to local media.
The town recorded a temperature of 49.3C (120.7F) at around 3pm local time on 27 December, according to the Bureau of Meteorology.
It was Australia’s highest temperature for 2018 in what was the country’s hottest year ever.
Sky News Australia’s meteorologist Rob Sharpe said although heat records have been broken, more look set to be smashed with the capital Canberra set to have its most intense heat in five years.
“A heatwave is now well under way across south eastern Australia,” he said.
Concerns have been raised about the health of tennis stars competing in the Australia Open in Melbourne which started on Monday.
Extra measures, including 10-minute heat stress breaks, have been put in place to protect the athletes.
Reports of swathes of fish dying because they are unable to cope with the heat and subsequent droughts have prompted Australia’s government to announce a $5m (£2.8m) recovery programme.
A fire ban has been introduced to some areas of the country over fears of a repeat of the bush fire deaths of 180 people nine years ago.