Dangers are more pronounced for Western Australia's southern regions, with fears hot, dry weather could intensify bushfires already burning on the outskirts of Perth.
The WA capital is on track for multiple hot days, the Bureau of Meteorology warns, with maximum temperatures of 37C possible on Saturday and 40C on Sunday.
Very hot and dry conditions are expected on Saturday with east to southeast winds, at times fresh and gusty during the morning over the ranges east of Perth.
High fire dangers are forecast for much of western WA for Saturday, with extreme fire danger warnings in place for three regions near Perth.
Conditions have improved for blazes on the fringes of Perth but WA Department of Fire and Emergency Services' Shaun Champ said the elevated temperatures across the weekend would be "very trying" for operations.
"If a fire was to ignite, putting pressure on the current fires we have in the landscape with those strong easterly winds coming off the desert, it is going to put pressure on containment lines," he told ABC Radio.
The potential for dry lightning was also a concern, most likely on Sunday.
Well-above-average temperatures and a severe heatwave developing along the west coast during the next few days will track south during the week.
Weekend heatwave warnings have also been issued for parts of the Northern Territory, South Australia and Queensland.
A reverse situation is expected to unfold in the country's east, with cooler weather and rain set to fall along the coast and across NSW.
A cold front will also cool down South Australia and parts of Victoria.
High fire danger and gale-force winds are forecast across much of Tasmania on Sunday.
Tasmania Fire and Emergency Services Commissioner Jeremy Smith said strong winds and isolated storms would compound the fire risk.
"A high fire danger rating means there's a heightened risk of fires, which can become dangerous and spread quickly," he said.
Mr Smith said with storms forecast, dry lightning was a concern for fire starts, mainly in the state's east.
Tasmania has already experienced fires on its southern and east coasts this summer and while the threat has eased, warnings remain in place, with Dianas Basin and Peron Dunes to be avoided on Saturday.
25°C