A "severe to extreme" heatwave will grip large parts of the country across the weekend, making conditions difficult for firefighters working to control catastrophic blazes in several states.
Bureau of Meteorology (BOM) maps show large parts of South Australia, Victoria and New South Wales are expected to experience temperatures in the high 30s to 40s over the weekend and into early next week.
Despite much of the country experiencing a brief reprieve over Christmas, the heat is currently moving through central-western Australia and is expected to reach the south-eastern parts of the country by Friday.
Victorian authorities are particularly concerned about three large bushfires burning in East Gippsland, which could affect communities from the Great Dividing Range to the coast.
It is feared the looming heatwave conditions will cause the fires to spread, and that dry lightning forecast from Friday to Monday could start more fires.
The state's emergency management commissioner, Andrew Crisp, urged holidaymakers to reconsider any plans to visit the region's parks and forests.
In South Australia, the threat level from the devastating Cudlee Creek fire in the Adelaide Hills has been downgraded to an advice message — however, the Country Fire Service is warning residents to stay alert.
Regional areas are likely to be the hottest on Monday, with Oodnadatta in South Australia peaking at 47 degrees Celsius, Swan Hill in Victoria expected to reach 43C, and Menindee in New South Wales forecast for 45C.
As for metropolitan areas, Parramatta in Western Sydney is expected to reach 39C on Monday and Tuesday; Melbourne is forecast to reach 41C on Monday; and the northern Adelaide suburb of Elizabeth could reach 41C on Friday, 40C on Saturday and 39C on Sunday and Monday.
Canberra is expected to reach 38C on Saturday and Sunday, before hitting 40C on Monday.
Tasmanians will not be spared from the heat — Hobart is predicted to hit 36C on Monday.
The forecast has prompted BOM NSW to warn people in affected areas to plan ahead and learn how to look after themselves and others in the heat.
The Australian Red Cross recommends people take cool showers, place a damp cloth on the back of the neck, stay indoors where possible, drink plenty of water, wear loose-fitting clothing and snack on cold foods such as fruit and salads.
Conditions easing — in some parts — before NYE
Current BOM forecasts show the heatwave beginning to ease in parts of South Australia, western Victoria and Tasmania by Sunday, with temperatures dropping into the mid-to-high 20s in most capital cities on New Year's Day.
However, eastern NSW and parts of northern WA will continue to face severe to extreme heatwave conditions up to Wednesday, January 1.
Dubbo is expected to be 42C on Tuesday and 40C on Wednesday, while further east, Muswellbrook is forecast to hit 44C on Tuesday before cooling slightly to 38C on Wednesday.
Sydney is likely to be milder, forecast for 33C on Tuesday and down to 26C on Wednesday.
Forecast comes during record-breaking December
The heatwave forecast comes just a week after Australia narrowly missed out on making it three in a row for its hottest-ever days, breaking temperature records in parts of Victoria, South Australia and the ACT.
Data from the BOM showed Tuesday, December 17 to be Australia's hottest day on record.
That day, the average maximum temperature across the country was 40.9C, breaking the mark of 40.3C set in January 2013.
PHOTO: Tradesmen in Victoria looked for ways to cool down due to recent record temperatures. (ABC News: Billy Draper)
South Australia experienced four days of extreme heatwave conditions — the highest rating level — with catastrophic bushfires sparking on Friday.
In New South Wales, about 100 homes were lost in bushfires over the weekend, but cooler conditions since Monday have allowed NSW RFS to plan containment strategies.
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.
The records last week were not just broken, but surpassed by big margins.
Professor David Karoly, a leading climate scientist at the CSIRO, said the cause was clear.