Sydney Weather: Dangerous heat wave set to hit today – here's how hot it will be in your city

A cool change is not expected to sweep across Australia until later this week, as large parts of the country prepare for even more sweltering heatwaves.

Dangerous heatwave conditions will persist across many parts of the country, with a cool change not expected until later in the week.

A wave of warm weather made some regions warmer, with temperatures peaking around 40 degrees on Tuesday.

But the wave is not over yet: the weather bureau predicts that maximum and minimum temperatures will be 5 to 12 degrees above average for the rest of the week.

For NSW, temperatures will reach the mid 30s to 40s during the day and low to high 20s at night, with the mercury highest on Thursday and Friday.

Severe heatwaves will develop in central and northern inland parts of the state, spreading eastwards towards Sydney, the Hunter and Mid North Coast on Wednesday and Thursday.

Armidale, Camden, Campbelltown, Hornsby, Liverpool, Moree, Nowra, Orange, Richmond and Wollongong will all bear the brunt of the heat.

Some regions in the north-west slopes and plains, such as Walgett, are expected to reach temperatures of 42 degrees Celsius, while parts of the upper western part of NSW, including Wilcannia, could reach a high of 46 degrees Celsius.

NSW State Emergency Operations Controller, Deputy Commissioner for Emergency Management Peter Thurtell urged people to watch out for heat stroke or heat exhaustion.

NSW Health warned that a severe case of heat stroke could result in 'permanent disability or death'.

“In extreme heat, your body's ability to cool itself can fail, causing your body temperature to rise to dangerous levels… Heat stroke requires immediate emergency medical care,” a spokesperson said.

'Symptoms include confusion, slurred speech, agitation and altered mental status, profuse sweating or warm, dry skin, muscle twitching or seizures, rapid breathing, a rapid strong pulse or a very high body temperature.

'Heat stroke is extremely dangerous and can quickly become life-threatening. If you are concerned about heatstroke, call triple-0 immediately.”

The health department advised people over the age of 65, infants and young children, people with certain medical conditions, people who work outside the home, pregnant women, people who live alone and people who are homeless are at greater risk of severe heat stroke.

Severe heatwaves are also forecast for the North West, North East and Flinders regions of South Australia, with some areas expected to see temperatures in the mid 40s.

It will be another scorching day for the southern state after the capital reached over 41 degrees Celsius on Tuesday afternoon, the first day above 40 degrees Celsius of the year.

Several cities have already experienced their hottest day this week, including Brisbane, which reached a temperature of 37 degrees Celsius on Monday, and Adelaide on Tuesday, which reached a temperature of 39 degrees.

Extreme fire danger is also forecast for parts of the Pilbara coast on Wednesday.

A cool change will develop later on Wednesday, with a low-intensity heatwave continuing across the northeast on Sunday, the Bureau of Meteorology said.