An RFS spokesperson said the fire was impacting near the truck stop at Jerrawangla.

"We have Fire and Rescue and Rural Fire Service strike teams in the area," he said.

"About a kilometre along the highway is unburnt. We are hoping to block it off and prevent more of these intermittent road closures."

The spokesperson said there was currently increased activity across the fireground, but containment lines were generally holding.

There has been another spotover north of the Shoalhaven River, to the west of Kangaroo Valley.