AN OUT-OF-CONTROL bushfire on the NSW south coast has burnt out almost 1,000 hectares of national park land. 

More than 100 firefighters and nine water bombing aircraft were fighting the blaze in a remote area of the Budawang National Park, about 30km from Batemans Bay.

The fire was sparked on Tuesday by a lightning strike.

A Rural Fire Service spokesman said there was no threat to property and crews were hoping the hot, gusty conditions with temperatures of 30 degrees would ease to allow backburning.

"We're looking at backburning this afternoon in an effort to contain the fire, if conditions are right," he said today.

He also warned people setting off to the south coast for the long weekend to expect heavy smoke on the Kings Highway.

"We're just advising people in particular between Braidwood and Batemans Bay that the road is open, but you can expect to see a lot of smoke, so slow down and drive to the conditions," he said.

A fire in the Morton National Park, about 25km from Nowra, was contained yesterday, but crews were still on the ground watching for signs of reignition.

"They'll remain there today just mopping up and going through the burnt area, rolling over the logs - just making sure that they are completely out," the RFS spokesman said.

"We are expecting a bit of hot weather of the next couple of days so we will keep an eye on it."

Eighteen smaller fires were still burning across NSW as heatwave conditions showed no sign of abating, with temperatures across much of the state to remain in the high 30s throughout the weekend.

AAP