A trifecta of dangerous weather conditions has prompted extreme to catastrophic danger alerts to be issued for parts of South Australia.
The Country Fire Service warned Friday would be "one of the most significant fire weather days in several years".
It comes as high or extreme fire danger is predicted in most of NSW, where heatwave conditions are due to continue for days.
Adelaide hit 29.6C before 7am on Friday, as temperatures across the state head towards the mid-40s.
Strong winds and dry lightning are also adding to the fire risk.
Catastrophic fire danger ratings was declared for the mid-north, Flinders, Yorke Peninsula, Riverland and eastern Eyre Peninsula districts, while five regions face extreme fire danger.
Any fires that did start would be "incredibly difficult" for firefighters to control, CFS chief officer Brett Loughlin said.
"The dry lightning creates a real risk of fire starting anywhere these thunderstorms occur, unfortunately the forecast is a broad area of dry lightning and thunderstorm activity," he told reporters on Thursday.
SA authorities say strong winds may prevent the use of aerial fire fighting assets. (Russell Millard/AAP PHOTOS)
The service secured a large air tanker from the Commonwealth to help with firefighting operations, but Mr Loughlin said conditions could hamper its use.
"I want to stress, the forecast winds tomorrow are such that there is likely to be times when an aircraft will be unable to safely fly and fight fires," he said.
"It is crucial that people do not rely on firefighters and aviation assets to save them."
Residents were urged to have a bushfire survival plan in place and to understand what they would do in the event of an emergency.
Electricity outages are also possible as equipment is set to disconnect to minimise the risk of sparking a blaze.
After Friday's heat, temperatures will dip to the low to mid-20s across much of SA on Saturday, with Adelaide forecast to have up to 60 mm of rain over the weekend.
A total fire ban is in place for several NSW areas west of the Divide for Friday, ahead of even warmer conditions on Saturday, when Sydney's west could hit 44C.
A Total Fire Ban in place tomorrow, Friday 8 December - Lower Central West Plains, Southern Riverina, Northern Riverina & South Western areas. Very hot, dry and windy conditions forecast across parts of NSW. Know what you'll do if fire threatens. — NSW RFS (@NSWRFS) #RFS https://t.co/R9tDns8ts6 pic.twitter.com/lNQEoHbxsEDecember 7, 2023
Meanwhile, the mercury didn't dip below 30C overnight in the outback town of Wilcannia as it sweats through a forecast 10-day streak of 40C days.
High temperatures sparked a warning to employers to protect their workers and develop a workplace heat-management plan to ensure safety.
"We don't want to see anyone needing medical attention due to heat exposure," SafeWork NSW head Trent Curtin said on Friday.
"Workers are reminded to listen to their body when the temperature rises and to drink plenty of water.
"It is vital you do not replace water with soft drinks, energy drinks or coffee as these can dehydrate you further. "
Unsafe practices can be reported in NSW via the Speak Up Save Lives app.
Parts of Queensland, West Australia, the Northern Territory and ACT have also copped soaring temperatures that are expected to intensify over the weekend.
15°C