Australia has just sweltered through at least five of its 10 warmest days on record, authorities estimate.
An extreme heatwave has afflicted the nation since Saturday, causing wildlife deaths, bushfires and an increase in hospital admissions.
Australia's Bureau of Meteorology said preliminary readings showed daily national temperature highs of 40C.
The town of Noona in New South Wales meanwhile recorded a night-time temperature of 35.9C.
It was the highest minimum temperature ever recorded anywhere in Australia, the Bureau of Meteorology (BOM) said.
Temperatures on Friday will soar above 42C in "broad areas", the bureau predicted.
Forecasters have compared conditions to the nation's worst heatwave in 2013, where the mercury soared to 39C for seven consecutive days.
The hottest day on record for Australia is 7 January 2013, when the national average maximum temperature was 40.3C.
"The current heatwave ranks alongside that of January 2013 as the most extensive and prolonged heatwave on record over Australia," BOM senior meteorologist Blair Trewin told the BBC earlier this week.
"There have been other notable heatwaves but none affecting such a large area of the country."
A large swathe of New South Wales is bearing the brunt of the heat, with temperatures also soaring in parts of Queensland, South Australia, Victoria and the Northern Territory.
Temperatures are expected to drop in southern and central areas over the weekend.