States have declared total fire bans across South Australia, Victoria and Tasmania ahead of the extreme heat. (Agencies)
Adelaide's maximum temperature on Tuesday is pegged to reach 41 degrees Celsius, with 40 Degrees Celsius on Friday, 41 Degrees Celsius on Saturday and 40 Degrees Celsius on Sunday, a report said.
A catastrophic fire danger rating has been issued for the state's lower south-east, the report said.
Country Fire Service state coordinator Brenton Eden said, "We are facing a horror day when we already have existing fires burning in the state."
In Victoria, some parts are expected to stay above 40 degrees Celsius for six days, while Melbourne will be in the 30s for much of the week.
Mildura in the state's north is expected to touch 40 degrees Celsius for a week while southern parts of Victoria will also have a period of extended heat.
States have declared total fire bans across South Australia, Victoria and Tasmania ahead of the extreme heat.