Most of the country has sweltered through a second straight day of higher-than-average temperatures, as a heatwave persists into its third day.

The Bureau of Meteorology earlier this week warned a record-breaking heatwave was on the horizon – and it wasn’t wrong.

Maximum temperatures in New South Wales, Victoria, South Australia and Tasmania are anywhere between eight and 16 degrees higher than the January average.

In outback NSW, the overnight minimum temperature on Monday night failed to dip below 33 degrees.

Temperatures were commonly seen reaching the early 40s – and as high as 46 – throughout NSW, Victoria and South Australia on Tuesday.

The severity of the heatwave is expected to lessen in Victoria, parts of South Australia and Tasmania on Wednesday, transforming to a low-intensity heatwave, according to the bureau.

NSW and the ACT, however, can expect hotter-than-average days for the rest of the working week and into the weekend.

The heatwave has prompted a range of warnings from authorities – including in South Australia and NSW, where residents were urged not to pick up any bats that have dropped out of their trees due to the heat. The state’s respective health bodies warned the creatures carry a bat-specific virus that, if bitten or scratched, can transmit rabies to humans.

The Red Cross issued a warning to Australians to be aware of their health in the high temperatures.

The national body’s emergency services manager Andrew Coghlan said most people wouldn’t know that more people die as a result of heatwaves than because of floods, bushfires or cyclones.

Mr Coghlan said older people, pregnant women, children, people living with disability, and those who take certain medications are more at risk of developing a heat-related illness.

“Everyone is affected by the heat in different ways, but there are some simple steps you can take to reduce the effects,” Mr Coghlan said.

“Top of the list is keeping out of the heat and making sure you drink water regularly.”

New South Wales: The worst is yet to come

While temperatures throughout NSW hovered in the high 30s and low to mid-40s, the bureau has warned Thursday and Friday are expected to bring the warmest days, with residents also being warned to brace for “oppressively hot” nights.

Eastern NSW is tipped to experience the brunt of the heatwave, while western Sydney will be searching for cool relief with temperatures set to hit 43 degrees in Richmond and 45 degrees in Penrith.

The bureau’s forecasting manager Jane Golding told media on Tuesday that temperatures would hover around 45 degrees at the Great Dividing Range, and those highs would slowly creep towards the coast as the week wore on.

She said while Sydney city would escape those extreme maximums, high humidity levels meant the nights would bring little cool relief.

Victoria: Hot on and off the court

Australian Open punters are being urged to prep for warm conditions throughout the week.

While maximum temperatures are expected to drop as the week goes on, the state’s emergency management commissioner Andrew Crisp advised tennis goers – or anyone attending an outdoor event this week – to wear a hat and sunscreen, and bring bottled water.

A total fire ban was active throughout the entire state on Tuesday. Mildura, on the NSW border, reached 45 degrees, while Melbourne hovered around the 30-degree mark throughout the day.

While many Victorians would be searching for relief in the depths of swimming pools, the state’s chief health officer issued a warning on Tuesday.

Dr Brett Sutton said there were 780 cases of a waterborne illness called cryptosporidium reported in the state last year – a germ that can cause respiratory and gastrointestinal illnesses.

“Even in the best-maintained pools, germs on your body can wash off and contaminate the water,” Dr Sutton said.

He said the best way to prevent the spread of the germ was for pool users to shower with soap before swimming, especially if they are experiencing feelings of ill health.

Queensland: Southwest swelters

The outback town of Birdsville is famous for its horse races. This week, it will also make headlines for its extreme temperatures, expected to peak at 46 degrees on Thursday.

Most of the southwest of the Sunshine State will feel maximums in the early 40s for the rest of the week, the bureau told AAP.

Brisbane escapes the worst of the wave, with comparatively cool temperatures in the low 30s.

South Australia: Alert issued

The State Emergency Service has issued an emergency warning for an extreme heatwave, and the state government declared Tuesday and Wednesday code-red days, which activates more funding for support services for the homeless.

It also means a specialist phone line will be in place, which will call and check in on the elderly and at-risk.

The state is expected to experience temperatures into the low 40s – including Adelaide – throughout Wednesday and Thursday until a cool change sweeps the state on Thursday afternoon.

Western Australia, the ACT and Tasmania

Western Australia is not expected to cop the worst of the heatwave until later this week, with the most severe of the temperatures to be concentrated around the greater Perth area from Friday and into the weekend.

In Tasmania, hot and windy weather was responsible for 1500 dry lightning strikes overnight on Monday, as severe but dry thunderstorms swept over the state.

Firefighters are continuing to battle a 20,000-hectare blaze in the state’s southern wilderness, and authorities have urged all residents to be on high alert for bushfires as temperatures continue to push into the high 30s this week.

Canberra and the ACT will piggy back NSW’s extreme temperatures of 40 and 41 throughout Wednesday, Thursday and Friday, before a cool change is tipped to bring lower temperatures and showers on Saturday.

The Northern Territory has escaped the worst of the extremes, with only a low-intensity heatwave forecast for the lower half of the territory for the rest of the week.

-with AAP