Residents across much of southern Australia are bracing for another heatwave, with temperatures forecast to reach into the 40s in some areas today.
Total fire bans have been issued across South Australia, Victoria and Tasmania ahead of the extreme heat.
Adelaide's maximum temperature today is expected to be 41 degrees Celsius, with 40C on Friday, 41C on Saturday and 40C on Sunday.
A catastrophic fire danger rating has been issued for the state's lower south-east.
Country Fire Service state coordinator Brenton Eden says the weather conditions in South Australia could not be worse.
"We are facing a horror day when we already have existing fires burning in the state," he said.
Firefighters have been battling the Bangor fire in the southern Flinders Ranges for a fortnight.
The hot and windy weather has also seen fire activity increase at the Billiat fire in the Mallee.
Extra water bombers have been stationed in the south-east and in the Flinders today.
Victoria on alert amid extreme conditions
Victoria is also on fire alert, with temperatures expected to reach 39C in Melbourne and up to 42C in the state's west.
The Country Fire Authority has listed an extreme fire rating for the South West and Wimmera regions, and says bushfires could become uncontrollable in today's extreme conditions.
Along with scorching heat, winds of up to 40 kilometres per hour are forecast for western Victoria.
"Those conditions would lead to fires being quite uncontrollable if a fire started," CFA spokesman Steven Walls said.
"Most of Victoria will be subject to potentially very significant fire conditions, so we are asking all Victorians to take particular care when they're outdoors with anything that might cause fires, that includes machinery."
A cool change will come through Melbourne tonight, but there is not any relief for the northern parts of the state for a week.
Weather bureau meteorologist James Taylor says conditions there will rival the heatwave experienced earlier this month.
"The fact that we're expecting seven days above 40 degrees indicates there is some chance that this heatwave could be slightly longer," he said.
Tasmanians warned of fire danger
Total fire bans are also in place across Tasmania, with temperatures in some parts of the state expected to reach the high 30s.
The Tasmanian Fire Service says any fires will develop quickly and be very difficult to control.
Chief fire officer Mike Brown says the worst of the fire danger ratings are for the Upper Derwent Valley, the east coast, and the south-east.
"Generally if we look at history we have the worst of our fire weather conditions generally around early February," he said.
"So that's one thing that's of concern to us while people are still holidaying and camping and enjoying outdoors in fine weather, when we get that really hot weather present itself with strong winds as well, that of course elevates the fire risk."
Heat prompts health warnings
Victorian Health Minister David Davis says the heat can have a serious impact on the health of the elderly.
He has asked the public to keep in contact with their older relatives today.
"It's really important that if you've got a neighbour, or a friend, or a family member who's older or vulnerable that you check in on them, that you see if there is something that can be done to help them," he said.
He has urged all people to respect the heat and avoid physical activity in the sun.
"If you are able to avoid strenuous exertion like sport or gardening at a time when the temperature is at its maximum do so. The heat can actually sneak up on anyone," he said.
© ABC 2014
16:15 EST The Bureau of Meteorology is warning Sydney and northern New South Wales could be in for another deluge, with a new low pressure system to form off the coast later this week.