(CNN) Australia is sweltering under record-breaking temperatures as an extreme heat wave continues to sweep across the country, causing wildlife to die and fruit to cook from the inside out.

The past four days are in Australia's top ten warmest days on record, the Australian Bureau of Meteorology said in a tweet on Wednesday, with all of the country's eight states and territories affected.

South Australia's Port Augusta hit a scorching 48.5 degrees Celsius (119 F) on Tuesday, the highest since records began in 1962, according to CNN affiliate Nine News . The town of Tarcoola in South Australia reached a sweltering 49 C (120 F).

Elsewhere, temperatures stayed well above 40 C (104 F) and the hot weather is expected to last until Friday. One town in northwestern Australia, Marble Bar, suffering through 22 consecutive days of temperatures above 40 C, at one point almost reaching 50 C (122 F).

As the mercury continues to rise, concerns are with the vulnerable, including the young, elderly and those with asthma or respiratory diseases.

High ozone levels

On Wednesday, New South Wales Health authorities warned that the high temperatures are expected to contribute to "high ozone" air pollution across Sydney.

Dr. Richard Broome, director of environmental health at New South Wales Health, said that people with asthma and other respiratory problems were particularly vulnerable as ozone "can irritate the lungs."

"Ozone levels are higher outdoors than indoors, and generally highest in the afternoon and early evening, so limiting time outdoors during the heat of the day and in the evening helps people to not only keep cool but to limit their exposure to ozone pollution," he said.

The past 4 days are in Australia's top 10 warmest days on record—and the trend looks like continuing today. The nights have been warm too, which is what defines #heatwave conditions https://t.co/u6dbfmKPk6 Stay cool, check on loved ones & follow advice from health authorities pic.twitter.com/8Qisw9m4LM — Bureau of Meteorology, Australia (@BOM_au) January 16, 2019

A health warning was in place across New South Wales from Tuesday, warning people to stay indoors during the hottest part of the day, minimize physical activity and keep hydrated.

"Signs of heat-related illness include dizziness, tiredness, irritability, thirst, fainting, muscle pains or cramps, headache, changes in skin color, rapid pulse, shallow breathing, vomiting and confusion," the statement said

It's the second heatwave in less than a month to hit Australia. Just over two weeks ago, a brutal post-Christmas heatwave led to extreme or severe fire warnings across at least three states and intensified severe droughts across the country.

Fish, bat deaths and fruit cooking from the inside

The high temperatures are taking an increasing toll on the country's flora and fauna. In the Murray-Darling River Basin across the southeast, more than a million dead fish have been washed up on the banks.

Niall Blair, Primary Industries Minister in New South Wales state, said more deaths of marine life are expected in coming days as temperatures continue to rise, according to local media

But environmental activists have blamed the mass deaths on poor management of the river system by state and federal governments, alleging mass consumption of water by farmers was leaving too little for fish to survive.

"A lack of water in the Darling River and the Menindee Lakes means that authorities were unable to flush the system before millions of fish suffocated through a lack of oxygen in water," independent New South Wales lawmaker Jeremy Buckingham said in a statement.

"This mass fish kill should be a wake up call for Australia."

Dozens of fish lying dead on the Darling River in New South Wales near Menindee after an extreme heat wave in January.

Colonies of bats were also succumbing to the heat and dropping from trees in Adelaide, according to CNN affiliate Nine News , prompting warnings to avoid contact with the animals as they can carry deadly diseases.

Heat can be disastrous for bat species. Following a heat wave in north Queensland in November, an estimated 23,000 spectacled flying foxes died -- almost one third of the species in Australia.

In South Australia, the extreme heat is causing stone fruit, including peaches and nectarines, to cook from the inside out, leading to heavy losses for farmers and spurring a race against time to harvest the fruit before it spoils, according to ABC.

"The stone burns them, which means they burn on the inside, they become squashy and you can't use them," Dried Tree Fruits Australia chairman Kris Werner told ABC.

It comes as the Australian Open kicked off in Melbourne at the Rod Laver Arena, in temperatures which topped 30 C (86 F).

It is the second year in a row of extreme temperatures at the Grand Slam event, with some competitors collapsing or complaining of heatstroke in the 2018 event.

Climate change taking its toll

January is typically the hottest month of the Australian summer and temperatures across the board have been higher in the country in recent years.

A report released by the Bureau of Meteorology on Thursday revealed 2018 was the country's third hottest year on record, with rainfall 11% below average.

Australia's winter last year saw the worst drought in living memory hit part of the country in August, destroying farmers' livelihoods as farmland turned dry and barren.

Even as Australia has suffered the effects of ongoing climate change, the government drags its feet on crafting a comprehensive environmental policy.