Extreme fire danger ratings are in place for Sydney and the Hunter region on Tuesday, as well as a swathe of the state's interior, stretching from the lower central-west plains to the Queensland border.
Temperatures reached 37.2C at Sydney Airport about 2.30pm on Tuesday, with the city centre, Penrith, Gosford and Nowra all cracking 35C.
Those highs are as much as 15C above the October average maximum temperatures for the same locations.
The hot conditions sparked dozens of new fires across the state on Tuesday afternoon, including one threatening Bermagui on the south coast during the busy school holiday period.
The rapid move east led to an emergency warning for the popular holiday town as well as neighbouring Cuttagee where it was impacting properties.
The NSW Rural Fire Service (RFS) said it was now too late for residents to leave and they should seek shelter inside a solid structure if in the two towns or Barragga Bay.
The same message was issued for a south-moving fire in bushland near Abernethy in the Cessnock region worrying authorities.
"I counted on a map at least a dozen spot fires ahead of the main fire - all in amongst properties," RFS Commissioner Rob Rogers Rogers told 2GB of the second blaze.
"It'll be a pretty anxious couple of hours for residents and crews."
The emergency warnings are among the first issued for this bushfire season, which is expected to be the worst since the 2019/20 Black Summer.
About 4.30pm, 91 blazes were burning statewide, including 15 out of control.
The largest uncontrolled blaze near Bredbo in the Snowy-Monaro region doubled in size to 875 hectares under strong winds as firefighters, heavy machinery and aircraft tried to strengthen containment lines.
It remained at watch and act level.
The threats come after some buildings and stock were destroyed by a fast-moving grass fire in the north of Mudgee in the central west on Monday afternoon.
Premier Chris Minns said forecasts of a "horrific" bushfire season was one of the things that kept him up at night.
"I don't want anybody to get over-confident - this could be a really tough bushfire season," he said.
Meanwhile, SES crews were also busy after on Tuesday after winds exceeding 100km/h tore roofs off hotels and ski lodges at Smiggin Holes, Lake Crackenback and Perisher Valley.
Flood, hail and significant rain warnings were also issued for Tuesday night and Wednesday in the Riverina and Snowy Mountain regions.
NSW FIRE DANGER FOR WEDNESDAY
Extreme: northern slopes*
High: Greater Hunter*, Greater Sydney, north western*, upper central-west plains, south western, far north coast, north coast, New England.
*denotes total fire ban
13°C