Temperatures across Australia's southeast are expected to reach above 40C as state authorities warn of 'catastrophic' bushfire conditions at the weekend.
In NSW, Surf Life Saving and the Rural Fire Service are warning residents to stay safe on the state's beaches and prepare for potential bushfires.
"Lifesavers and lifeguards are out in force but we need the public to take some responsibility for their own safety," Surf Life Saving chief executive Steven Pearce said in a statement on Friday.
"The tragic incidents we have witnessed through December and early January are a reminder of the power of the ocean."
The RFS is warning residents of an elevated fire danger and wants people to prepare properties now.
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"We will be monitoring these conditions very closely, especially any changes in wind, and there is the potential for conditions to deteriorate further on Sunday in areas including Sydney and the Hunter," NSW RFS commissioner Shane Fitzsimmons said in a statement.
"Our advice is simple - monitor conditions, know the fire danger for your area, and know what you will do if there is a fire."
Parts of NSW are tipped to reach 45C on Saturday - including Menindee in the far west and Ivanhoe in the state's centre.
Most of the state will swelter through temperatures above 40C on Sunday including Bulahdelah on the mid-north coast which is set to reach 45C.
Sydneysiders will avoid the worst of the heat with temperatures forecast to peak at 38C in the city on Sunday when Penrith could hit 45C.
The temperatures are not unusual for summer in NSW, bureau forecaster Peter Zmijewski told AAP on Friday.
Endeavour Energy has reassured customers it has specific plans in place for hot days with emergency response crews on standby in case of equipment failure.
'This heat is a killer'
Meanwhile Melbourne is forecast to reach 41C on Saturday, with northerly winds reaching up to 40km/h.
This will make it the hottest day the city has experienced since January 13, 2016, when temperatures soared to 42.2C.
Geelong and Bendigo are forecast to reach a high of 42C on Saturday, and Avalon, Echuca and Warracknabeal 43C.
"This heat is a killer. It's going to be like a blast furnace tomorrow and you need to adjust what you do," Ambulance Victoria's state health commander Paul Holman told reporters on Friday.
"You need to take this seriously. You need to take care. So put off the sporting events, put off the outside events, stay inside."
There is a total fire ban across the state on Saturday, and those planning on camping and bushwalking have been told to be aware of potential bushfires and heat stress.
Heat health alerts have been issued for three Victorian districts as authorities expect a dangerous heatwave.
With crowds expected to flock to the beach to cool off, Life Saving Victoria is warning people to look out for rips, and to swim in a sheltered spot.
Four people have drowned on the state's coastlines since Christmas Day.
'A recipe for fire'
South Australian authorities are bracing for catastrophic bushfire conditions across the state with soaring temperatures and high winds.
Emergency Services Minister Chris Picton says the conditions on Saturday will be among the worst since the 2015 Pinery fire, north of Adelaide, which claimed two lives.
Mr Picton says the Country Fire Service will be on its highest level of alert, the state emergency centre will be activated and additional water bombing aircraft will be brought in from NSW and Victoria.
The Bureau of Meteorology says catastrophic conditions are likely to be declared in the Mt Lofty Ranges and in the southeast and extreme conditions will prevail in most other districts.
Total fire bans will be in place for the entire state.
Adelaide will have a top temperature of 41C while the mercury will reach the mid-40s in some regional and outback towns.
CFS chief officer Greg Nettleton said the combination of high temperatures, strong winds and low humidity raised the risk of any fires getting out of hand.
"High temperatures, low humidity, strong winds, fuel, it's all there," he said.
"A recipe for fire."
The Pinery fire raged through 86,000 hectares of scrub and farmland killing 56-year-old Janet Hughes and 69-year-old Allan Tiller.
Another 90 people were hospitalised while 91 houses and almost 400 other buildings were destroyed.
Total fire ban for Tasmania
Further south in Tasmania, authorities are also bracing for severe bushfire conditions in parts of the state on Saturday, with hot and windy weather expected.
Temperatures are forecast to reach the mid-30s in the Apple Isle's east and south with wind gusts of up to 45km/h, the Bureau of Meteorology predicts.
A total fire ban will be in place for King Island and northern and southern Tasmania for all of Saturday.
"Grass and forest fuels are extremely dry and in abundance. Combined with hot, dry and windy weather, this makes controlling fires extremely difficult," Tasmania Fire Service state fire controller Jeremy Smith said on Friday.
"(The ban) means no fire in the open, campfire or anything. If you've had a campfire or fire on your property, please ensure it's fully extinguished."
More than 200 fire brigades are on standby across the state, with specialist response teams and aircraft also ready to go.
Tasmania Police are checking in with known and suspected arsonists in a bid to prevent any fires being sparked.
A deliberately-lit bushfire threatened homes in George Town, near Launceston, this week but was controlled by firefighters.
Hobart is expected to reach 34 degrees on Saturday.
A cool change is expected to sweep across the island state on Sunday, dropping temperatures by as much as ten degrees.
