'Silent killer': heat on health as hot spell drags on

Australians are being warned an ongoing heatwave in many parts of the nation is a public health emergency and lives are at risk.

From Queensland to South Australia, states are roasting in an extended heatwave that has shattered records as the mercury soars towards 50C in many areas.

Severe to extreme inland heatwave conditions in the inland are expected to persist into the weekend before easing.

The prolonged and frequent heatwaves needed to be treated as a public health emergency, health expert Kate Charlesworth said.

"Heat is a silent killer,'' said Dr Charlesworth, from the Climate Council.

"It has killed more Australians than all other extreme weather events combined - with more than 1000 lives taken during heatwaves between 2016 and 2019."

Extreme heat warnings have been issued for Victoria, NSW, Queensland, South Australia and the ACT.

Locations likely to be impacted include Broken Hill and Bourke in NSW, Roxby Downs and Marree in South Australia expected to reach 49C, Birdsville and Thargomindah in Queensland as well as Canberra and Belconnen in the ACT.

The severity of Victoria's heatwave, where bushfires have been raging, is comparable to previous ones in January 2009 and January 1939, the Bureau of Meteorology's David Crook said.

Data from the bureau shows a long-term increase in heatwave frequency and intensity particularly since the year 2000 because of climate change.

Victoria's Emergency Management Commissioner Tim Wiebusch said the state would get eight consecutive days with temperatures above 40C.

Victoria smashed its own heat record as Walpeup in the state's north hit 48.9C on Tuesday.

It has also been a particularly scorching week for Wilcannia in northwest NSW with temperatures hitting more than 47C for three days in a row and predicted to reach the same mark on Thursday.

The NSW Rural Fire Service has issued a total fire ban for the Northern Slopes region for Thursday amid a forecast for hot, dry and windy conditions.

The fire ban, which begins at midnight, covers Gunnedah, Gwydir, Inverell, Liverpool Plains and Tamworth.