Firefighters are on high alert with parts of Australia tipped to have seven days above 40C.
Roxby Downs and Oodnadatta in South Australia's outback are set to sizzle with six days in a row above 45C and the tiny town of Tarcoola is forecast to reach 47C on Monday.
Temperatures will remain above 40C for the next six or seven days in many other inland parts of Australia including the towns of Mildura and Ouyen in Victoria.
Victoria is set to experience its longest stretch of heat and some of its worst fire conditions since Black Saturday when 173 people died.
Many towns in eastern Western Australia and western Queensland will also feel the heat, with temperatures set to soar into the 40s in parts of both states.
Even Hobart won't escape the warm weather with 38C predicted on Friday.
Firefighters in Victoria are preparing for one of the worst days since Black Saturday.
Country Fire Authority state duty officer Brett Boatman says conditions on Friday will be extreme in parts of Victoria.
"It is certainly one of the higher fire danger days I have seen since Black Saturday, no doubt," Boatman said.
UNUSUAL HOT SPELL
The heatwave is expected to be one of the largest heatwaves in decades after coming off a sharp shift in 2012 from wetter to drier-than-average conditions.
''We have a major heat event under way,'' Karl Braganza, manager of climate monitoring at the Bureau of Meteorology, said. ''There are not many instances in the historical record where you get a heat event covering such a large area of the continent.''
Brett Dutschke, senior meteorologist at Weatherzone, said it was unusual to have so prolonged a hot spell. ''It's a once-in-20 or 30-year heatwave event in desert areas,'' he said. ''More populated areas further south ... are going to experience some of this as well.''
Much of south-eastern Australia has weathered warm temperatures for months. ''We effectively had midsummer heat arriving at the end of spring,'' Dutschke said.
Nationwide, though, 2012 was probably an average year, temperature-wise, with the Bureau of Meteorology due to release figures today.
The rainfall shift, though, was stark. Much of the continent went from cool and wet in the March quarter to drier-than-average conditions within a short spate of time.
"The stunning reversal in rainfall from wet to dry across large parts of the continent, particularly the south, is a result of a switch from a La Nina (weather pattern) early in the year to El Nino-like conditions through winter and spring," Braganza said.
- AAP and Sydney Morning Herald