Heathcote bushfire first of the season for RFS water-bomber named Marie Bashir

The blaze has now burnt more than 400 hectares of national park land to the east of the highway, after being sparked by a spot fire from a hazard reduction burn being conducted by National Parks to the west on Saturday.

NSW Rural Fire Service pokesperson Greg Allan said around 90 firefighters were working to control the fire, and were being assisted by six aircraft.

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"Crews were assisted by water-bombing aircraft - especially on the northern side of the fire - due to the difficult terrain, it's very difficult to get trucks in there and crews on foot," Mr Allan said.

"We've had to via helicopter get our specialist firefighters to those northern parts, who have worked extremely hard today [Monday] to control that fire ... with the hope that today we will have this fire contained."

The Transport Management Centre advises motorists to reduce their speed and exercise caution if there is smoke.

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Once the blaze is contained, crews will continue to patrol the fireground until it is completely extinguished and "mop up".

"Turning over logs, making sure there are no hotspots or flare-ups," Mr Allan said.

"There could be a little bit of smoke noticeable ... but no major threat."

He said this was the first fire of the season for their 737 airtanker "Marie Bashir" to be used, which was utilised on both Saturday and Sunday.

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