Australia’s southeast coast is set to swelter through a couple of gruelling days as temperatures soar across Victoria, South Australia and Tasmania.

After two weeks of brutal heat, Sydneysiders will receive somewhat of a reprieve with a looming cold front coming through on Sunday.

But for those further down the coast, authorities are warning that the conditions could prove fatal.

“There will be scores of people who have cardiac arrest or who present in a really severe state by ambulance,” Victoria’s acting Chief Health Officer Brett Sutton said.

Meanwhile parents are again being told not to leave children in the car on hot days, as they could be unconscious in minutes.

Victoria: ‘If a fire starts it’s going to be uncontrollable’

Victorians are set to bake and firefighters are on high alert with thunderstorms, strong winds and fire risks adding to the potentially deadly conditions.

Mildura, Swan Hill, Kerang and Echuca in the state’s northwest, are tipped to hit 46C while Bendigo heads to a top of 45C and Melbourne is forecast to reach 42C on Friday.

A cool change will bring welcome relief for some areas later in the day but may bring wind gusts up to 100km/h with the potential to exacerbate fires.

Thunderstorms are also expected in parts of central and eastern Victoria in the late afternoon, with the possibility of dry lightning strikes posing a risk of fire.

A total fire ban has been issued for Victoria with extreme fire warnings for the Mallee and the Wimmera.

“If a fire starts it’s going to be uncontrollable, it’s going to be fast-moving,” Emergency Management Commissioner Andrew Crisp said.

SA swelters through a scorcher

South Australia has sweltered through a summer scorcher with temperatures in the west and northern parts of the state soaring into the mid-40s.

Ceduna, on the state’s west coast, was among the hottest spots with the mercury reaching 47.1C on Thursday.

Other centres were almost as hot including Oodnadatta with 46.3C, Nullarbor with 46.2C and Port Augusta with 45.5C.

In Adelaide the top at the Kent Town observation centre hit 42.3C.

But the Bureau of Meteorology said a cool change was slowly edging across SA and dropped the temperature by 10 degrees at Nullarbor in just eight minutes.

The cooler conditions are expected to reach Adelaide during Friday morning with the city forecast to have a milder top of just 31C ahead of even cooler conditions across the weekend.

The Country Fire Service reported no major incidents with the worst being a fire in a hay truck at Auburn in the mid-north.

Unseasonably warm in Tassie

Tasmanians are preparing for a day of scorching, dry and windy weather, with authorities warning of a severe fire risk for parts of the island state.

Hobart is expected to reach 36 degrees on Friday, with Campania and Brighton tipped to hit 39.

“Those temperatures are 10 to 15 degrees warmer than what we’d expect at this time of the year,” climatologist Ian Barnes-Keoghan said.

Extra firefighters and equipment are on standby, with the east coast, southeast, midlands and Upper Derwent Valley rated a severe fire risk.

A total fire ban is in place for the eastern half of the state.

The mercury is likely to peak around 2pm, before an afternoon cool change brings relief to Hobart and sweeps up the east coast.

Friday is the sixth anniversary of the Dunalley bushfires that destroyed hundreds of homes in the state’s southeast.

Popular national park tracks at Mt Field, Freycinet and Maria Island have been closed due to the extreme heat.