The mercury has climbed to a record 48.9C in the outer western Sydney suburb of Penrith.
The western Sydney suburb of Penrith was the hottest place on Earth on Saturday, reaching a high of 48.9 degrees Celsius.
The highest-ever temperature for the area, recorded by the Bureau of Meteorology just after 3pm, smashed a record that had stood for 80 years.
At the same time, world temperature map website World Weather Today showed Penrith was the hottest place in the world.
Three hours later, at 6pm, the website showed the places with the top ten highest temperatures recorded globally over the previous 24 hours were all in Australia.
Penrith’s temperature also set a new record for the Sydney basin, beating the previous mark of 47.8 degrees in Richmond in 1939.
Canberra also broke records as the mercury climbed to 43.6 degrees on Saturday afternoon.
The previous Canberra record was 42.8 degrees at the now-closed Acton observation site in 1939.
The nation's capital has been choked with smoke from bushfires for days, with the hazardous air pollution forcing shops and attractions to close.
Conditions across Sydney and southern New South Wales were expected to worsen through Saturday evening, with a cool change expected to hamper firefighting efforts.
The southerly change was expected to reach inner Sydney at 11pm, then the Blue Mountains by midnight.
A cool easterly change was expected in Canberra at around 10pm.
Additional reporting by AAP.