Large parts of Australia sweltered through Boxing Day and will continue to roast through Tuesday as a heatwave sets in across the country.

The Bureau of Meteorology issued heatwave warnings for New South Wales, Victoria, Western Australia, South Australia and Tasmania on Monday, with temperatures expected to stay high until Wednesday.

The heatwave is particularly fierce in southern parts of Australia, with minimums and maximums sitting at eight to 16 degrees Celsius above averages.

The forecast sweltering heat got off to an early start on Boxing Day with the mercury speeding past 20 degrees early in the day.

Canberra got to 29 degrees before midday, while Sydney and Melbourne reached 25 and 23 degrees respectively.

Adelaide was sweating through 34-degree heat at noon local time and Perth residents woke up to a 23-degree morning and eventually it reached 26 degrees.

In coming days, most of Victoria will either sweat through a low-intensity heatwave or a severe heatwave – the first proper one of a summer that has so far been relatively cool.

“[There will be] maximum temperatures reaching the mid-to-high-30s and overnight minimum temperatures in the high teens to low-20s across Victoria,” the bureau said.

“The heat will peak … with mid to high-30s, reaching 40 in the north-west. A cool change from the west will ease heatwave conditions from Wednesday.”

Tweet from @BOM_au

On Tuesday, the Bureau of Meteorology said Melbourne could reach 37 degrees before dropping back down to 30 on Wednesday.

In NSW, the heatwave warning applies across the south coast, Snowy Mountains, south-west slopes, Riverina and lower Western Districts.

The BoM said southern, inland parts of NSW could reach the mid to high 30s.

“The heat will peak over most parts on Tuesday as maximum temperatures reach 40 over southern inland parts,” the Bureau said.

“Heatwave conditions are expected to ease on Wednesday and Thursday following the passage of a cool change.”

In Sydney, the temperature will be in the high 20s for the next few days. Monday will be the hottest with a top of 29 degrees.

Much of the country is going to have hot weather over the coming days.

Adelaide the hottest

Adelaide is forecast to be the hottest capital in Australia, with a top of 40 degrees on Tuesday.

A severe heatwave warning is in place for South Australia’s Riverland, Murraylands, west coast, Lower Eyre Peninsula and north-west pastoral districts.

The temperature should drop down to the mid-20s by Wednesday, bringing some much-needed relief.

Tasmania won’t escape either, with a severe heatwave engulfing much of the state in coming days.

Maximums will be in the mid to high-20s, with coastal areas getting temperatures in the low to mid-30s on Tuesday.

Across the north-west to south-east of Western Australia, the temperatures will be in the high-30s to mid-40s.

Perth should have maximums in the mid-20s in coming days, though there is a high fire danger risk in the capital.

Tweet from @SA_SES

How to handle a heatwave

Heatwaves can be deadly. The bureau says severe and extreme heatwaves have killed more people than any other natural disaster in Australia.

“Heatwaves can be dangerous because they pose health risks to the most vulnerable, such as elderly people and very young children,” the bureau says.

During a heatwave, people are advised to seek out a cool place, such as a home, or something public like a library or shopping centre.

If at home, people should shut all windows and draw all blinds, curtains and awnings early in the day to keep out the heat.

If available, people should make use of fans or air-conditioners to cool down.

The Australian Red Cross advises people to take cold showers or splash water on themselves multiple times a day.

Even if you’re not thirsty, drink plenty of water.

During a heatwave, alcohol, fizzy drinks, coffee and tea should be avoided, as they can make dehydration worse.

Heat stroke is a life-threatening emergency and 000 should be called if anyone shows signs of it.

Symptoms include fits, confusion, staggering, and people could collapse or fall unconscious, the Australian Red Cross said.

with AAP