Temperatures have surged past 40C across NSW, combining with gusty winds to create "catastrophic" fire conditions.
The Southern Tablelands towns of Goulburn, Yass and Braidwood set December maximum temperature records on Saturday while, further west in the ACT, Canberra recorded its highest December temperature of 41.1 degrees.
Near the geographical centre of NSW, Condobolin nudged 46.4C, while the mercury soared to 47 degrees in western Sydney at Penrith and Richmond.
"There's some very significant heat out there," Bureau of Meteorology forecaster Agata Imielska told reporters.
"Quite a number of areas have recorded temperatures of 45 degrees and above."
A southerly wind change rolled across the state on Saturday afternoon, dropping temperatures but elevating fire danger at key locations.
RFS commissioner Shane Fitzsimmons said the southerly's intensity would deteriorate away from the coast but make life harder for firefighters.
He said Saturday was an "awful" day for firefighting but milder conditions should arrive after the southerly moved through.
Temperatures in NSW will cool in coming days as the heat pushes up into Queensland and the Northern Territory.
Victoria on Friday sweltered through its hottest December day on record, while the mercury reached 49.2C in the town of Keith in South Australia.
Australian Associated Press