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."

The southerly change is making its way up the coast of NSW and has reached Nowra with 75km/hr gusts recorded. The change will push many fires in a generally more northerly direction and create dangerous conditions. People should be prepared. #nswrfs #nswfires pic.twitter.com/sXfyxjktzt — NSW RFS (@NSWRFS) January 4, 2020

Firefighters remain 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".

"We are in for a long night ... we are still yet to hit the worst of it," she told reporters at the RFS headquarters in Sydney.

This is when the southerly hit Nowra earlier this afternoon. The video shows the dramatic change in the colour of the sky from the Currowan Fire.

My parents in North Nowra are remaining vigilant for embers and spot fires. #NSWbushfires#Shoalhaven#firesNSWpic.twitter.com/P2BTzpyZGp — Steven (@booragal) January 4, 2020

Power outages

NSW residents have been urged to limit their electricity usage after bushfires damaged critical infrastructure particularly in the Snowy Mountains.

Energy Minister Matt Kean has asked everyone to be mindful of unnecessary usage after transmission lines failed in the Snowy region on Saturday.

People should turn off pool pumps, set air conditioners to 24 or 25 degrees Celsius and avoid using washing machines and dishwashers.

"The extensive bushfire activity in the Snowy Mountains and other areas of the state have had an impact on our electricity supplies," Mr Kean said in a statement.

Some 150 fires are burning across NSW with half uncontained. Thirteen were at emergency warning level in southern NSW at 7pm while nine were at "watch and act".

Earlier, RFS commissioner Shane Fitzsimmons said the worst of the weather was yet to eventuate.

AAP

"It's a very dangerous few hours given the amount of emergency alerts that are out there," he told reporters about 5pm.

About 3,600 firefighters are on the ground battling blazes while hundreds of others have been positioned to tackle any new outbreaks.

Mr Fitzsimmons said some large fires were generating their own thunderstorms which could generate cyclonic-type winds.

In some areas, firefighters had been withdrawn for their own safety.

Fire on the Princes Hwy north of Moruya. NE winds are keeping the situation at bay at the moment. @SBSNews #nswfires pic.twitter.com/CrzbYqXaKz — Cassandra Bain (@CassyBain) January 4, 2020

"Under these conditions suppression is unachievable," the RFS commissioner said.

"The focus becomes saving lives and saving property as much as we can."

Mr Fitzsimmons said he'd be surprised if homes weren't destroyed before the night was over.

Emergency warnings are in place for fires in the Snowy Monaro and Snowy Valley regions as well as on the South Coast and at the 268,000-hectare Green Wattle Creek blaze southwest of Sydney.

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A dangerous fire-generated thunderstorm has formed over the Currowan fire between Nowra and Batemans Bay which could spark new blazes.

Hospitals in Batlow, Pambula and Tumut were evacuated as were healthcare facilities in Tumbarumba and Delegate.

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Regional Express airline suspended all South Coast services on Saturday morning due to the extreme bushfire conditions.

Liberal Bega MP Andrew Constance - who planned to defend his home on Saturday - said the region could be "smashed".

A statewide total fire ban has been in place on Saturday as is a week-long state of emergency - the third in as many months.

A statewide fire ban has also been issued for Sunday "due to forecast warm and windy conditions".

Eight people, including a firefighter, have died in NSW since Monday. Another man, seriously burnt in a bushfire in November, died in hospital on Sunday.