Authorities are bracing for more property losses following another destructive bushfire day in which temperature records were broken.

Key points: A "volatile" wind change is making its way up the NSW coast

A "volatile" wind change is making its way up the NSW coast Residents in parts of the state's south are being urged to take shelter

Residents in parts of the state's south are being urged to take shelter Premier Gladys Berejiklian said NSW was "yet to hit the worst of it"

Weary fire crews worked well into the night battling blazes fanned by a predicted southerly change that swept up the east coast, hitting parts of Sydney around 10:00pm.

During the worst of the day there were 13 emergency warnings across the state, while the mercury in Penrith, in Sydney's west, reached 48.9 degrees Celsius — a new record temperature for the Sydney Basin.

NSW residents were urged to reduce their power usage after bushfires took out transmitters in the Snowy Mountains.

The NSW Rural Fire Service has received preliminary reports of at least 15 properties lost across the fire grounds — including in the towns of Batlow and Talbingo in the NSW Snowy Mountains, and in Manyana on the South Coast.

Fire and Rescue NSW said it responded to reports of 20 people trapped at the caravan park in nearby Bendalong and was able to free them after extinguishing fires in three homes in the suburb.

Firefighters battle a blaze at Numbugga, about 15 kilometres from Bega. ( ABC News )

But Commissioner Shane Fitzsimmons said he expected more.

"Some [firefighters] are reporting at least 15 properties alight in some locations [today]," he said.

"We just don't have that intelligence at the moment.

"The focus really is on moving resources around, trying to save and protect what we can and deal with what is unfolding and fast-moving fires still occurring down in that south eastern quadrant."

Fire burns at North Bendalong on the NSW South Coast. ( Supplied )

Late into the night, Eden on the Far South Coast came under threat from fires across the border in Victoria. The Southern Highlands towns of Wingello, Penrose and Bundanoon were also threatened by fire.

Many seeking shelter at the Bundanoon oval received a police escort into Bowral and Mittagong.

Commissioner Fitzsimmons said preliminary reports suggested fire was sitting about 2 kilometres west of Kangaroo Valley.

He said while the southerly change would see temperatures plummet by up to 20 degrees Celsius on Sunday, steady winds and bone dry fuel loads meant fire crews could not be complacent.

While crews battled blazes across the state, emergency services responded to reports in the southern NSW town of Cooma of the collapse a 4.5 million-litre water reservoir, with one woman suffering a minor injury.

Police said water flowed through the town's streets, with water damage to houses and vehicles, including one car that was swept 800 metres down the road.

A bushfire approaches Cambewarra. ( Supplied: Glenn Tyson )

Earlier, Commissioner Fitzsimmons warned the southerly change would bring "volatile" winds of around 80 kph.

Premier Gladys Berejiklian said there hadn't been any reports of lives lost but it was a "very volatile situation".

A fire comes dangerously close to a home in Berrara. ( ABC News )

Bega in darkness at 6:18pm as smoke fills the sky. ( ABC News: Phil Williams )

The Princes Highway, that connects Sydney and Adelaide, remained closed in both directions near Jervis Bay and drivers in some places were warned to avoid all non-essential travel.

The RFS warned a fire-generated thunderstorm had formed over one fire in the Snowy Monaro area creating a "very dangerous situation".

The South Coast towns of Bendalong and Manyana have been impacted by fire. ( Ingleside Rural Fire Brigade )

'It's very scary'

New South Wales Transport Minister and Member for Bega, Andrew Constance — who has been defending his home against ember attacks — compared the South Coast fires to "an atomic bomb".

"I've got to be honest with you, this isn't a bushfire, it's an atomic bomb," he told ABC Radio Sydney.

"It's indescribable the hell it's caused and the devastation it's caused."

Darcy Lay said the Bega Valley town of Bermagui was like a ghost town and the colour of the sky was "terrifying".

"Getting told to move from Bermagui so quickly and anxiously, in a panic, it's very scary. We really need a lot more done about these fires down here," Mr Lay said.

Brothers Darcy and Jasper Lay say they're feeling the stress of fires in Bermagui. ( ABC News: Baz Ruddick )

He said it wasn't smart to stay there, particularly if emergency services were moving out.

"The heat is just going to be too immense … it's just not realistic to be in a town where the heat and the smoke is going to absolutely pummel and plume the town."

He said they hadn't had power in a week.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 24 seconds 24 s Smoke fills the sky abover Batemans Bay, while in a supermarket shelves sit empty

"We've lost thousands of dollars' worth of stock," he said.

"Stock is replaceable. Houses are replaceable. Lives are not replaceable."

Julianne Domeny fled to Batemans Bay with her two daughters, mother-in-law, a friend and her sons, leaving their husbands to protect their Broulee homes.

"We have been at Broulee since the New Year's fires hit and we saw a ball of fire coming straight at us," she said.

"We thought we were completely prepared for that … but seeing the devastation, after that, we prepared everything."

The NSW death toll since the start of the bushfire season is 17, including eight since Monday and at least 449 homes destroyed on the South Coast since New Year's Eve.