(CNN)Australians are sweltering in temperatures as much as 12 degrees Celsius (21.6 Fahrenheit) above average after another extreme heatwave swept across the country Monday, the second in under a month.
New extreme heat wave hits Australia causing temperatures to soar
Temperatures rose above 40 C (104 F) at the weekend and the extreme weather is expected to last the week. Forecasts show all of Australia's eight states and territories are expected to be affected by the extended heatwave.
"Plan to keep yourself cool, check in on family and friends and follow the advice from your local health authorities," the Australian Bureau of Meteorology said on social media.
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.
One town in northwestern Australia, Marble Bar, has now had 22 consecutive days of temperatures above 40 C, at one point almost reaching 50 C (122 F).
The high temperatures are taking an increasing toll on wildlife. 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."
The heatwave is forecast to continue to hit southeastern Australia, including Sydney and the rest of New South Wales, in coming days.
By Friday it should have mostly eased, according to Bureau of Meteorology forecasts.
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.
Temperatures across the board have been higher in Australia 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.