New South Wales state Bureau of Meteorology said it had initially believed the heat to be an all-time record, topping one from February 2017, where temperatures edged 47C.
A away from the countryside and the authorities have had to transfer scores of homeless people to hospitals for treatment as temperatures in city of Sydney reached a scorching 47.8 degrees Celsius.
The previous record was set in 1939, when Richmond station in the city's west topped out at 47.8C.
It's going to be another hot day for Sydney with temperatures. You need to take care.
New South Wales Police Deputy Commissioner Catherine Burn said the state's heat wave plan had been activated to respond to "severe to extreme heat conditions".
"We've seen over the past month, fires that we've had haven't necessarily been burning on days of severe or above-fire-danger rating. the fuel is dry out there, the fuel's dry all around NSW".
"Meantime with the arch rivalry between the Australian and English cricket teams being played-out in the Ashes Test Series at the Sydney Cricket Ground (SCG) meteorologists advised fans to "#slipslopslapseekslide".
There's a total fire ban in place for the Greater Sydney and Hunter regions, as much of Australia's east struggles through the record heatwave.
The hashtag refers to an old sun safety campaign - "Slip on a shirt, slop on sunscreen and slap on a hat".
That's the second hottest day in Sydney's 158 years of recorded history.
There's some relief in sight however, with temperatures predicted to be slightly "colder" Monday - a maximum of 33 degrees Celsius or 91.4 degrees Fahrenheit for those hunkering down in the cold further north.