Updated | Large air tanker called in to help control bushfire hazard reduction operation south of Heathcote

Water bombing aircraft will continue to support firefighters trying to contain a bushfire in Royal National Park near Waterfall, which started as a hazard reduction burn.

The 737 Large Air Tanker 'Marie Bashir' was called in on Saturday afternoon to combat the fire, whch caused severe traffic disruption on Princes Highway.

The Rural Fire Service said in an update on Sunday morning the fire on Kangaroo Ridge was burning on the eastern side of the Princes Highway, south of Heathcote.

"There has been minimal fire activity overnight and this morning, with no current threat to property," the statement said .

"Firefighters will again be assisted by water bombing aircraft today, to assist crews working to control the fire, particularly in difficult terrain on the northern edge of the fire.

"The Princes Highway is open in both directions under reduced speed."

Update

The 737 Large Air Tanker 'Marie Bashir' was called in to help control a hazard reduction burn between Heathcote and Waterfall at Heathcote, which caused severe traffic disruption on Princes Highway this afternoon.

This is the first use of the aircraft this fire season.

The Rural Fire Service said there was still no current threat to property.

Earlier

Motorists on Princes Highway in the Waterfall area experienced extensive delays on Saturday afternoon when a bushfire hazard reduction burn spread beyond containment lines.

The burn took place on the western side of the highway between Heathcote and Waterfall, but spot fires broke out on the eastern side of the highway.

The area was covered by thick smoke.

Southbound lanes on the highway and one northbound lane were closed for periods.

The Rural Fire Service said in a statement: "NSW RFS crews are assisting NSW National Parks and Wildlife Service at a hazard reduction burn in the Royal National Park near Waterfall to the west of the Princes Motorway," a statement said.

"There has been an increase of fire activity and the fire has spotted to the east.

"Smoke will be visible in the area.

"Traffic may also be affected on the Princes Motorway in both directions.

"Please avoid unnecessary travel in the area. There are no current threats to property. Please only report unattended fires to Triple Zero (000)."