More than 100 homes in a New South Wales town are under threat as extreme weather hampers firefighting efforts across the state.

And officials warn more scorching temperatures are on the way.

Late this afternoon an emergency warning was issued for residents near the township of Rylstone .. 50 kilometres east of Mudgee in the state's central west.

A blaze from the northern edge of the Windermere Dam is burning in extreme fire danger conditions about eight kilometres from Rylstone .. with more than 100 homes at risk.

Across the state .. about 70 fires are burning .. mostly in remote and inaccessible terrain in the Blue Mountains .. the Hawksbury region and in the state's north.

The fires were sparked yesterday after record-breaking heat, lightning storms and wild winds which continued today, with Premier Nathan Ree saying it has never been this hot, dry and windy.

Meanwhile, the fire threat in Victoria and South Australia has eased as cooler weather and a rain band sweeps across southern Australia.