As mercury continues to rise, concerns are among the vulnerable, including young, elderly and people with asthma or respiratory diseases.
High ozone levels
On Wednesday, New South Wales health authorities warned that high temperatures are expected to contribute to high ozone air pollution throughout Sydney.
"Ozone levels are higher outdoors than indoors and generally highest in the afternoon and early evening, so limiting time outdoors in today's heat and evening helps people not only stay cool but to limit their exposure to ozone pollution," he said.
There was a health warning across New South Wales on Tuesday that warns people to stay indoors during the hottest day of the day, minimize physical activity and keep hydrated.
It's the second heat wave in less than a month to hit Australia. Just over two weeks ago, a brutal post-heat wave led to extreme or severe fire warnings across at least three states and intensified severe droughts across the country.
Fish, bats and fruit cooking from within  The high temperatures take 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, Prime Minister of the New South Wales State, said several marine life deaths are expected to come days when temperatures continue to rise, according to local media.
But environmentalists have blamed the mass deaths on the poor management of the river system by state and federal governments. The claim that farmers' mass consumption of water was too little to fish for survival.
"Lack of water in the Darling River and Menindee lakes means that the authorities could not rinse the system until millions of fish are stifled by lack of oxygen in water," independent lawyer New South Wales Jeremy Buckingham said in a statement.
"This mass death killer must be a wake-up call to Australia."
"The stone burns them, which means they burn on the inside, they become squashy and you can't use them." Dried tree fruits Australia President Kris Werner told ABC.
This is the second year in a row with extreme temperatures at the Grand Slam event, where some competitors collapse or complain about heat radiation in 2018
Climate change takes its toll
January is typically the hottest month in the Australian summer, and the temperature across the board has been higher in the country in recent years.
CNN's James Griffiths helped report.