Strong winds are set to wreak havoc across parts of Tasmania again on Friday, as other sweltering states can expect a cool change.
Tasmanian firefighters are battling hazardous fire conditions on Friday with conditions peaking at 5am Friday morning due to strong winds and dry air.
Melbourne can expect temperatures to exceed 40C on Friday, before thunderstorms and a sudden cool change sweeps the city after 3pm.
South Australia can expect some relief from the sweltering heat with Adelaide expected to reach a maximum of 31C on Friday.
Eight new fires in Tasmania
Residents in parts of southern and central Tasmania are being told to leave their homes ahead of early-morning hazardous fire conditions.
Eight new fires started on Thursday, adding to 50 others across the state with two-thirds considered uncontained, as authorities braced for worsening conditions.
The hazard is set to peak from 5am on Friday, with hours of dry air, temperatures reaching into the high 30s, and 40km/h winds gusting up to 90km/h.
"The best thing people can do in these conditions is leave early," the Tasmania Fire Service warned.
"A fire under the expected conditions can move very quickly with the potential for embers starting fires up to 20km ahead.
"Even those whose homes are well prepared to defend against fire will find their property is not defendable in these conditions."
Adding to the challenge for fire crews on Friday, forecast winds mean water-bombing aircraft will be grounded.
"The weather tomorrow may see that our aerial assets that have been so vital to us over the past week or so, are not able to fly," regional chief Jeff Harper said.
"The wind conditions are so turbulent that rotary-wing and fixed-wing aircraft, it's not safe for them to fly under those conditions."
Ground crews will be stepped up to try and cover the loss of aircraft, but Mr Harper said efforts will be prioritised in terms of human safety and property defence.
They are battling a combined fire front of more than 800km and since late last month, some 64,000 hectares of land has been burned.
Several fires have the potential to threaten communities. A blaze at central Great Pine Tier could bear down on the township of Shannon and the Gell River fire southwest of Hobart - which has been burning since December 28 - could reach Geeveston.
Victorian outages under investigation
Thousands of Victorians spent the hottest night in a year without power, with temperatures expected to climb into the 40s on Friday.
Many were without power as the temperature struggled to dip below 30C, with about 5800 properties affected by outages on Thursday night.
A spokesman for the State Control Centre said the cause of the outages was under investigation.
The blackouts came after Energy Minister Lily D'Ambrosio urged households to ration their non-essential electricity use.
While "absolutely confident" there was enough energy supply to get through the night, Ms D'Ambrosio suggested turning off dishwashers, kitchen appliances, washing machines and pool pumps.
"What we are asking Victorians to do is just be aware and be mindful that the activities we undertake when we're home do put that further pressure on our energy system," she told reporters on Thursday.
Records broken in South Australia
A cool change will bring much-needed relief to Adelaide on Friday, after hot weather records tumbled under sweltering conditions across South Australia.
The CBD recorded Australia's hottest capital city temperature when it reached 46.6C at 3.36pm on Thursday.
The reading was half-a-degree higher than its previous record of 46.1C set in January, 1939.
But the mercury rose even higher across the state, with Port Augusta the hottest at 49.5C and the fourth hottest temperature ever recorded in South Australia.
The town was one of more than 20 locations to experience record-breaking highs, others including Ceduna at 48.6C, Port Pirie and Whaylla at 48.5C.
Relief will come in the form of a cool change on Friday, when a maximum of 31C is forecast for Adelaide.