Several huge bushfire erupt in NSW, homes threatened south of Sydney

NSW firefighters are battling several serious blazes, with one threatening homes in the southern tablelands and another having forced the closure of the Royal National Park in Sydney's south.

An emergency warning has been issued for the out of control fire south of Bundeena. The park has been closed with visitors advised to leave only if it is clear to do so or if directed by emergency services.

Embers are believed to have caused a second fire nearby on Sir Bertram Stevens Drive at Flat Rock.

All roads into the Royal National Park have been closed and motorists are advised to avoid the area.

Further south, near Bowral, rural properties in the Alders and Crees Road areas in Bannaby may soon come under threat from a grassfire, the NSW Rural Fire Service says.

The 90-hectare blaze is at watch-and-act alert level with firefighters and an aircraft on scene to try to slow its spread.

A watch and act alert has also been issued north of Tamworth, where there's an out of control 3500-hectare fire. The RFS is concerned isolated rural properties may be threatened 10km southwest of Bundarra.

East of Canberra, ACT firefighters have been sent into NSW to protect houses threatened by another bushfire in the Southern Tablelands.

Three heavy tankers backed by smaller crews were deployed to the 274-hectare Braidwood blaze on Saturday morning after it burned through the night.

"Their objectives are to protect properties, attack and contain the main fire and contain spot fires," the ACT Emergency Services Agency said.

Meanwhile, firefighters continue to battle a fire that's burnt about 20,000 hectares in the Pilliga Forest between Coonabarabran and Narrabri.

The fire is at an advice level with no homes under threat but residents urged to monitor conditions.

Firefighters are conducting backburning operations in the area and the Newell Highway is shut between Narrabri and Coonabarabran and likely to remain closed on Saturday.