Major bushfires burning in NSW

A large uncontained bushfire in a national park south of Sydney has been declared an emergency, the NSW Rural Fire Service (RFS) says.

The fire, started by a lightning strike on Sunday in the Morton National Park has already burnt about 300 hectares of forest.

RFS Commissioner Shane Fitzsimmons said the blaze was declared a bushfire emergency about 3pm (AEDT) on Tuesday but no properties were yet at risk.

"It's reached proportions that require a lot of resources and a lot of coordination," he told AAP.

"Given that it's burning in very remote, rugged terrain, which is extremely difficult to access, there is a lot of challenge for the fire managers to identify appropriate containment lines and bring that fire under control."

The fire was moving east and there was currently no threat to nearby properties, Mr Fitzsimmons said.

Firefighters from the RFS, National Parks and Wildlife Service and Forests NSW are working with seven aircraft to contain the blaze.

Bulldozers and graders are also operating around the perimeter of the fire to establish containment lines on the northwest and southwest edges.

Hot winds, low humidity and soaring temperatures are making the bushfire difficult to control.

Firefighters have responded to a number of bushfires across the state on Tuesday as temperatures soared to the high 30s and low 40s.

Another major bushfire continues to burn near Singleton, in the Hunter Valley, on national park and private land.

The blaze covers more than 100 hectares and is also in rugged terrain, making it difficult to contain.

A fire south of Goulburn, which has been burning since Monday, has been contained but is expected to flare up again with hot winds.

Aircraft and tankers are being used to battle the blaze, along with 40 firefighters.

"We're finding that there's still active fire within those containment lines but we do have containment lines around that fire," the spokesman said.

Four other fires at Wollondilly, south of Sydney, Corowa, in the state's south, Bland in central NSW, and Coffs Harbour on the north coast, were now under control, he said.