More than one in three NSW towns recorded their hottest September day on record as summer arrived early across the state.
Areas of Sydney's west reached 36C while Bega smashed its previous record by three degrees when it hit 35.4C.
About 1pm, the Central Darling town of Wilcannia became the first NSW area in recorded history to reach 40C in September.
But it wasn't alone for long with fellow far west towns Bourke, Gumbalie and White Cliffs cracking the sweltering mark before 3pm.
The Bureau of Meteorology estimates roughly 40 per cent of weather stations had their hottest September day.
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"It was pretty phenomenal really," senior forecaster Jake Phillips told AAP.
"For this time of year, it's been very unusual."
Mr Phillips said the uncharacteristic conditions were spread across the state with parts of the Riverina falling just short of 40C and Orange's 26.8C exceeding its record by 2.5C.
Richmond, Badgerys Creek and Camden rewrote the record books in the Sydney area with 36C.
Sydney city reached 32.2C about 2pm - more than 11C higher than the September average top temperature.
More heat is predicted for Sydney and the northeast of the state on Sunday.
A total fire ban has been declared for much of those areas with Sydney is forecast to reach 33C.
Temperatures will ease after the weekend before heating up again mid-week.
A weak rain band is forecast to cross NSW on Thursday or Friday.
