The Comberton fire was upgraded again to Watch and Act about 11.30am Sunday with activity increasing in the Worrigee area, while the Tianjara and Currowan fires were downgraded to advice late Saturday.

On Sunday, the Rural Fire Service said at least two houses had been destroyed on Braidwood Road at Tianjara. There are reports of multiple properties lost in Nerriga, although that is yet to be confirmed and the RFS is assessing the situation.

RFS Southern Tablelands zone operations officer Lachlan Gilchrist told the Goulburn Post on Sunday it appeared some property had been lost, "but we are still attempting to assess the extent".

"It's a very dynamic situation because the fire is still very active and crews are focused on property protection and keeping people safe. It remains a concern."

Mr Gilchrist said with a south south-easterly wind blowing in from the coast, the fire could burn for weeks in the area.

"It is linking up with the Tianjara fire to the north, which is a very significant blaze burning more to the north and northwest. There is a lot of national park around there and if it reaches there, we won't get to it from a resources perspective," he said.

Wandandian Rural Fire Service captain Dennis Stannard said a new fire spotted over on Saturday afternoon from the Tianjara bushfire to Conjola National Park, to the east of the Princes Highway.

Firefighters aimed to use cooler conditions in the next two days to contain the fire, while watching the Tianjara fire on the western side of the highway in case it breached containment lines.

The Tianjara bushfire breached an escarpment to the west of Wandandian on Saturday.

A fire front now stretches from north of Wandandian south to Jerrawangala.

"It's quite a large front now to the west of the highway," Mr Stannard said.

Meanwhile, Prime Minister Scott Morrison returned from his holiday in Hawaii, and apologised. He also said it was not the time to be point-scoring.

Rural Fire Service commissioner Shane Fitzsimmons said 59 fires remained uncontrolled across NSW on Sunday morning.

He said Saturday night had been "volatile" for firefighters, who dealt with southerly gusts causing erratic behaviour across many firegrounds in NSW. But conditions were more favourable on Sunday morning thanks to lower temperatures, higher humidity and easterly winds.

The Princes Highway remains open, but both Braidwood Road and Turpentine Road are closed in both directions. The Kings Highway is also closed on the Clyde Mountain, and Live Traffic says it is expected to remain closed "until further notice". The Hume Highway reopened on Saturday evening after being closed because of fires near Bargo.

So far, the Currowan has burnt more than 140,000 hectares, Tianjara 21,000 ha and Comberton 249 ha.

The Currowan fire is burning between Burrill Lake and Morton National Park in the north, Braidwood in the west, and Batemans Bay in the south.

The Tianjara fire is burning towards Turpentine Road. Comberton burns around Forest Road.

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The more benign conditions come after a fire-generated thunderstorm formed over two South Coast fires on Saturday evening creating "a very dangerous situation" for crews on the ground, the NSW Rural Fire Service said.

On Saturday night, the Currowan fire burning west of Ulladulla was at emergency level and conditions had deteriorated to form the storm above it and the Tianjara fire. Visibility was severely reduced for fire crews on the ground.

The Tianjara fire was downgraded to watch and act as temperatures dropped and spots of rain fell on the South Coast on Saturday evening.

Saturday's extreme and unpredictable conditions caused flames in some areas to reach 60 metres in height.

The northern firefront of the Currowan fire impacted Nerriga about 6pm and residents sheltered in the pub that was being heavily defended, a Rural Fire Service spokesman said.

Just after 7pm the spokesman confirmed the fire had moved past the town. NSW Rural Fire Service spokesman Richard Thorek said the heritage museum, township homes and critical infrastructure had been protected but they were unsure of the losses outside of the immediate township.

"It's still smoked in, crews haven't been able to make an assessment as to whether anything has been damaged. The fire did go through there intensely so we are expecting some property losses," Mr Thorek said.

The Bungendore Rural Fire Service posted images showing the defence of Nerriga. It said a dozer put a containment line in just before the fire hit, and firefighters defended the properties.

The fire was moving into the Willow Forest Road area and people in that area were urged to remain vigilant and shelter in place. Erratic spot fires were occurring in the vicinity of Tudor Valley Road and Cargills Lane near Braidwood and while conditions had eased residents were told to be aware of any changes to the situation.

Further east, south of the Kings Highway, crews were responding to isolated flare-ups.

"The biggest area of concern is still around Nerriga, and parts of the Nerriga end of Oallen Road where a number of properties are still under threat," the spokesman said.

Residents of Oallen Road near Nerriga were advised to be vigilant through the night and be prepared for the fire to impact. Crews were working in those areas to secure the perimeter of the fire.

On the opposite side of the firefront to the north-east, people in Sussex Inlet, Lake Conjola, Yatte Yattah, Manyaya, Bendalong, Fishermans Paradise and Cunjurong Point were told it was too late to leave and to seek shelter as the fire approached.

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The Tianjara fire was burning towards Wandandian and Jerrawangala and people in those areas were also told it was too late to leave.

The Comberton fire near South Nowra remained at watch and act on Saturday night, but the Princes Highway was reopened. Residents near the fire were being warned to be vigilant for spot fires and ember attacks.

Sunday's fire danger will be high in the ACT, Far South Coast and Illawarra/Shoalhaven region. After a record setting temperature on Saturday, a top of 28 degrees is forecast for Canberra.