Australia's south-eastern states look set to endure up to three days of scorching temperatures, with the mercury in some parts expected to rise above 40C.
The Australian Bureau of Meteorology has issued hot weather warnings for NSW, Victoria and South Australia as temperatures look set to soar above 40C in the next three days.
Bushfire warnings have been issued for parts of each state, with particular emphasis placed on looking after the elderly and people with medical conditions.
Play at the Australian Open in Melbourne may be affected if temperatures surpass 40C, with referees having the discretion to stop matches, in line with the tournament's extreme weather policy.
Cyclists' competing at the Tour Down Under in South Australia have also been placed on high alert.
Here's how each state will fare as the mercury rises:
Residents in NSW are being urged to make a bushfire survival plan as temperatures are set to rise above 40C across parts of the state in coming days.
With severe heatwave conditions predicted for NSW in the coming days, residents have been encouraged to develop a bushfire survival plan.
The Bureau of Meteorology has warned of extremely hot conditions across much of the state from Friday to Sunday and severe fire danger warnings have been issued for several regions including Sydney.
NSW Rural Fire Service spokesman Greg Allan said people should make their own bushfire survival plan as each household has different needs.
"Planning to have a plan is not a plan. You've actually got to sit down, work out plan," he told AAP.
"As we saw with that fire just north of Newcastle, these things can start and spread pretty fast," he said of the blaze that forced the closure of Newcastle Airport.
Temperatures are set to soar in western NSW on Thursday with Wentworth near Mildura reaching 42C and Broken Hill reaching 41C.
But the real heat is set to hit on Friday and the weekend while much of the state swelters in temperatures in the high 30s and parts of NSW reaching the mid 40s, BOM forecaster Jonathon How said.
The heat, he said, is the result of a hot-air mass making its way through the south-eastern part of Australia.
On Saturday the mercury is set to top 45C at Hay and Ivanhoe in western NSW and 43C in Penrith in western Sydney.
Ivanhoe will again swelter on Sunday with temperatures rising to 46C, while Scone in the Hunter region reaches 44C.
"Penrith and Richmond have already had eight days above 40C so far this summer, so they're well on the way to beating the all-time record of 12 days over 40C," Mr How said.
The NSW RFS has issued a severe fire danger warning for Sydney, the central ranges, northwestern NSW, the Illawarra, the Hunter and the southern and northern slopes on Thursday.
Tourists, campers and other holidaymakers in unfamiliar environments are urged to take extra care, especially when swimming, police warned on Thursday.
Victoria: 40C+ hottest in three years
Temperatures in Melbourne are expected to climb to 39C on Friday, the Bureau of Meteorology says, with regional towns expected to crack 40C.
Forecaster Jonathan How said the hot burst isn't unprecedented.
"The last time this happened was in 2015, so for many people, it will be a bit of a shock because we haven't had these conditions in over three years," Mr How said.
Total fire bans have been declared for Thursday in several parts of the state including the Mallee, Wimmera, South West, Central and North Central areas and health warnings have been issued.
Emergency Services Minister James Merlino said the state was as prepared as possible but he urged Victorians to stay cool.
Play at the Australian Open may be affected as on-court temperatures look set to nudge 40C and above.
The tournament’s Extreme Heat Policy can be applied at the referee’s discretion when “the ambient temperature exceeds 40C and the Wet Bulb Globe Temperature index reading (which measures humidity) exceeds 32.5C”.
Environmental Law lecturer at Macquarie University Paul Govind said authorities need to consider measures to make sporting stadiums and precincts cooler during times of extreme heat.
"What we need to look at is the welfare of spectators in particular. some initiative may include shade, especially the use of trees and adequate ventilation," he told SBS News.
"We need to look at ways to reduce the accumulation of heat, so using materials that don't accumulate heat, such as, roof flooring, ventilation. Those are the kinds of design features that are needed."
Dr Govind said climate change would lead to hotter temperatures, and that facilities needed to adapt to rising temperatures.
South Australia: 27C+ at night, 40C+ days
The needs of the elderly, frail, young and those with cardiac and kidney complications could stretch medical services during South Australia's three-day heatwave, SA Health says.
Temperatures hit 41C in Adelaide early Thursday afternoon and are unlikely to dip below 27C overnight as the state braces for another scorcher on Friday.
SA Health spokesman Paddy Phillips said it was those people most at risk who accounted for the extra heat-related calls to ambulance services and hospital presentations.
"So far our hospitals are coping very well but it's over a prolonged period of heat where it's hot during the day and the night that the numbers do increase," Professor Phillips told reporters.
"The main thing is, take care of yourselves, take care of your neighbours and your friends and your work colleagues."
Temperatures in regional centres were even hotter on Thursday, the mercury hitting 43.5C at Pallamana, 43.4C at Port Augusta, 43.3C at Port Lincoln and 43.2C at Whyalla.
The heat forced organisers of the Tour Down Under cycling race to cut short Thursday's third stage.
Race director Mike Turtur said riders and officials agreed to cut the Glenelg to Victor Harbor stage by 26km to ensure the safety of all concerned, including spectators.
The Bureau of Meteorology said the blast of hot weather was being fuelled by a very hot air mass being dragged down from central Australia.
As a result, extreme bushfire conditions were declared in two SA districts with seven more considered extreme.
The conditions also prompted the Australian Energy Market Operator (AEMO) to issue a lack of reserve notice for short periods on both Thursday and Friday afternoon.
However, no major power outages had been reported and Energy Minister Tom Koutsantonis remained confident the state was well prepared and electricity supplies would be sufficient.
Queensland, Tasmania and WA
Queensland, Tasmania and Western Australia look set for much cooler temperatures over the weekend.
Perth is expecting it's hottest day on Saturday as the mercury looks set to reach a high of 33C.
Queensland's southern regions look set for temperatures in the early 30s, with central areas expecting seasonal norms nudging towards the late 30s.
Hobart is set for a high of 33C on Friday, before showers push temperatures to 20C on Saturday.