A man has died of cardiac arrest while trying to defend a friend's home from a bushfire.

The 47-year-old man was confirmed dead by NSW Premier Gladys Berejiklian at a press conference on Sunday morning.

Watch the video above

He had driven to Batlow, on the edge of the Great Dividing Range, from Goulburn on Saturday.

The unidentified man fell ill while battling fires, with thick smoke lingering in the air.

He collapsed in a nearby car and is believed to have gone into cardiac arrest.

Police and other emergency personnel rendered first aid but he was unable to be revived.

Watch the video below: NSW RFS Commissioner Shane Fitzsimmons gives an update on the NSW fires

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"Very sadly one person lost their life due to a cardiac arrest just outside of Batlow last night," Berejiklian said.

"Of course, our hearts, thoughts and minds go to their families during this very difficult time."

It brings the death toll from the bushfire season to 23.

Six people remain missing in Victoria and dozens more properties are feared lost in NSW. Credit: AAP

Batlow, a town of about 1,400 people was largely evacuated on Thursday and Friday.

Fewer than two-dozen people reportedly remained behind to defend their homes.

Four firefighters were also injured while on the line of duty overnight.

More from 7NEWS.com.au on the bushfire crisis:

According to Rural Fire Service Commissioner Shane Fitzsimmons, two suffered severe smoke inhalation and heat exhaustion in Milton, one suffered heat exhaustion in Cessnock and another suffered serious burns to their hands.

All were taken to hospital and discharged on Sunday morning.

He also estimated the property loss from Saturday night's fires was in the hundreds.