Temperatures have hit highs of 47.3C in the suburb of Penrith
People have flocked to the beach and tennis players been forced off court on Sydney's hottest day for 79 years.
The mercury hit 47.3C (117F) on Sunday in the suburb of Penrith.
Experts from the Australian Bureau of Meteorology - perhaps befuddled by the sweltering conditions - initially said it was metropolitan Sydney's hottest day ever.
#SydneyHeat According to preliminary data #Penrith has broken the all time maximum temperature record for both this station and the Sydney Metropolitan area with 47.1 degrees at 1:55pm. Previous record 47.0 on 11/2/2017. Latest observations: https://t.co/GORSOnwOjj.— Bureau of Meteorology, New South Wales (@BOM_NSW) January 7, 2018
But they later corrected themselves, admitting they had "missed a 47.8C temperature recorded at an old Richmond station (now closed) in 1939."
Sunday's scorching high was, however, still a record in Penrith.
The top temperature had initially been forecast as 40C (104F), but temperatures at the Sydney International tennis tournament exceeded that by 10am, forcing players off court.
At the Sydney Cricket Ground, spectators removed their shirts as they watched the fifth Ashes Test between Australia and England.
The greater Sydney area was given a severe fire danger rating, local media reported, while much of the rest of the state was issued with a very high rating.
Extra load on the network contributed to power outages at more than 4,000 properties in the New South Wales Central Coast region, electricity provider Ausgrid said.
The conditions are in stark contrast to those in the US, where a big freeze has left airports struggling to cope.