Temperatures push beyond 40 degrees Celsius in several states, as police investigate the potential deliberate ignition of a fire near Melbourne.
A hot air mass is pushing temperatures into the 40s across the country from the Kimberley region in Western Australia to Melbourne in the south.
While hot weather is not unusual in Western Australia, the Bureau of Meteorology has labelled it an "extreme heatwave" as the temperatures are unusually high.
The temperature at Fitzroy Crossing in the north of the state is expected to break records and hit 47 degrees on Saturday.
High temperatures in Victoria also means the state will record its hottest start to summer in 24 years, according to the Bureau of Meteorology.
It comes as police investigate the potential deliberate ignition of a fire which sparked an emergency evacuation alert in Victoria, where the threat remains amid changing winds.
The grass fire near Little River, 50km southwest of Melbourne, started from three separate points just before midday on Friday and quickly burned southwards.
"Victoria Police are looking into it but it's very, very early days in relation to the investigation," Emergency Management Commissioner Andrew Crisp told reporters when asked of the fire's cause.
The inferno crossed a rail line, halting train services bound for Geelong.
Nearby residents were ordered to evacuate, with a respite centre set up nearby.
As the threat eased, residents of Brophys Crossing, Cocoroc, Point Wilson, Werribee South, Little River, Mambourin, Tarneit and Wyndham Vale remained on high alert pending changing conditions.
Near Ballarat, crews continue to battle high winds as they fight a bushfire that started Thursday.
The blaze has destroyed a shed after it spread south from Nash's Road at Buninyong and scorched more than 40 hectares on Thursday afternoon, sparking an emergency warning.
As of Friday afternoon it remained under control but authorities warn locals to stay alert and monitor conditions, issuing a watch-and-act message for Durham Lead, Grenville and Scotsburn.
Winds were gusting up to 70km/h across the state including around Buninyong.
A severe fire danger is forecast for the Mallee, Wimmera and Northern Country districts.