Some areas of the states of New South Wales, Victoria and South Australia had temperatures above 40 C (104 F) on Thursday -- the fourth day in a row.
Extreme and severe fire warnings have been issued for parts of South Australia, Victoria and Western Australia, according to the Australian Bureau of Meteorology.
"The cause of the heat is a dome of high pressure settling in over much of the continent over the past few days," CNN meteorologist Gene Norman said.
"In addition to the sweltering temperatures, there is an enhanced fire risk in Victoria, with total fire bans declared for Thursday in the Mallee and Wimmera regions. South Australia has bans in place in 10 areas including the Mount Lofty Ranges and Yorke Peninsula. Western Australia has total fire bans in 13 districts, where temperatures are expected to exceed 45 C in parts."
CNN Meteorologist Brandon Miller added that Australia has recently issued an alert that El Nino conditions appear to forming over the Pacific Ocean.
"El Nino, which is characterized by a warming of the tropical waters in the Pacific Ocean, brings warmer and drier conditions to much of Australia, especially in the southeast," Miller said.
January is typically the hottest month of the Australian summer, and many fear the early heatwave may be the prelude to even more extreme weather in early 2019.
Sydney endured its hottest temperature in nearly 80 years in January 2018, with the mercury rising to 47.3 C (117.14 F) -- just half a degree off the all-time recorded high of 47.8 C (118.04 F) in 1939.
Super-high temperatures at the start of this year put a big strain on wildlife, with thousands of flying foxes dying due to dehydration, while an unusually hot and dry winter saw severe droughts hit part of the country in August.
Even as Australia has suffered the effects of ongoing climate change, the government drags its feet on crafting a comprehensive environmental policy.
Despite a report from the Intergovernmental Panel on Climate Change warning of "global catastrophe" should world temperatures rise above 1.5 C by the middle of the next decade, Prime Minister Scott Morrison's administration has refused to phase out the use of coal-fired power.
"I'm very much supportive of the coal industry," Deputy Prime Minister Michael McCormack told Sky News in October.
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