Authorities fear there's been "significant damage and destruction" in NSW with dozens of buildings potentially lost as a number of bushfires continue to create emergency conditions across southern parts of the state.
NSW Rural Fire Service Commissioner Shane Fitzsimmons on Saturday night said they were starting to hear of properties alight as firefighters continued to battle extreme bushfires.
He believed property losses could run into the dozens.
"Right across these fire grounds we are increasingly getting reports of significant damage and destruction," he told ABC TV.
"Some areas alone are reporting at least 15 properties alight in some locations."
RFS Deputy Commissioner Rob Rogers late on Saturday night said properties were believed to be lost in the Batlow area and North Nowra, and there were also reports of properties impacted at Bundanoon in the Southern Highlands.
He told ABC TV there were a lot of problems in the Snowy Mountains region, while a fire that had come across the Victorian border was threatening the southern town of Eden.
Firefighters are focused on saving what they can as a southerly change sweeps up the coast from the Victoria border and fire-generated thunderstorms worsen the situation.
Premier Gladys Berejiklian earlier on Saturday evening warned people facing extreme bushfires "it's not safe to move, it's not safe to leave these areas".
The situation was "very volatile" with southerly winds gusting up to 80km/h as the change moved up the coast.
It was expected to reach Sydney about midnight and Taree about 5am Sunday.
"Conditions are deteriorating rapidly," the Bureau of Meteorology tweeted.
"The gusty forecast southerly is pushing north and will continue along the coast tonight. Smoke plumes are triggering storms."
A wind gust of 128 km/h was recorded at Cabramurra in the western Snowy Mountains. It also recorded an incredible top temperature of 69.8C at 4.30pm.
"The situation appears to be that an intense pyro-cumulonimbus cloud formed above an intense fire to the east of Cabramurra during the afternoon," the bureau said in a statement explaining the temperature spike.
NSW Energy Minister Matt Kean said power could be turned off to parts of the state after bushfires destroyed transmission lines in the Snowies.
"There may be a need to turn off power in parts of the network to keep the overall system secure," the minister said in a statement.
Some 143 fires were burning across NSW on Saturday night. Twelve were at emergency warning level in southern NSW at 9pm while 10 were at "watch and act".
Some 3600 firefighters were on the ground battling blazes while hundreds of others were pre-positioned to tackle any new outbreaks.
Mr Fitzsimmons confirmed some large fires were generating their own thunderstorms which could generate cyclonic-type winds.
In some areas, firefighters had been withdrawn for their safety.
"Under these conditions suppression is unachievable," the RFS commissioner said.
"The focus becomes saving lives and saving property as much as we can."
Emergency warnings were in place on Saturday night for fires in the Snowy Monaro and Snowy Valley regions as well as on the South Coast and at the 271,683-hectare Green Wattle Creek blaze southwest of Sydney.
The mercury climbed to 48.9C in Penrith - a new record for the Sydney basin beating the previous mark of 47.8C recorded in Richmond in 1939.
Hospitals in Batlow, Pambula and Tumut were evacuated as were healthcare facilities in Tumbarumba and Delegate.
A statewide total fire ban is in place on Sunday while a week-long state of emergency - the third in as many months - continues.
Eight people, including a firefighter, have died in NSW in the past week. Another man, seriously burnt in a bushfire in November, died in hospital last Sunday.