Startling vision has emerged of a Fire and Rescue NSW crew forced to shield themselves inside their truck while passing through a bushfire emergency zone on the state's South Coast that encircled their vehicle within seconds.

The truckload of Central Coast firefighters from Station 509 in Wyoming had been driving through an intensely bushfire-affected area south of Nowra when flames quickly approached them.

In footage taken from inside the vehicle, rapidly-moving embers can be seen blowing all around the truck as it drives along the eerily glowing-red fire front.

A Fire & Rescue NSW crew has been forced to shield themselves inside their truck as they passed through an Emergency fire front zone. (Twitter)

Visibility ahead of the crew is then reduced to just metres as they slowly continue down a road before the flames - which had been burning as high as trees just moments before – appear directly beside the truck.

The crew is then instructed to put a protective flame-resistant mat up against their windows to stop any embers or fire entering the inside of the truck's cabin.

9News reporter Chris O'Keefe explained just how intense the conditions the firies faced were.

"This is what the firefighters are calling a flashover - that means the air is so hot and everything around it is at a temperature so high that it simply explodes," said O'Keefe.

"The firefighters here have to put up a blanket for themselves. They're worried the side of the truck could melt, the glass could cave in. The temperatures are like an oven."

Falling embers and a wall of flame can be seen rapidly approaching the vehicle as they drove down a road south of Nowra on the NSW South Coast. (Twitter)

Within moments, flames as tall as trees can be seen directly outside the fire truck. (Twitter)

The Currowan Emergency-level bushfire burning south of Nowra has now torn through more than 229,000 hectares of land and has crossed containment lines as it continues to rage out of control.