The Currowan fire was burning at advice level on Monday morning. It continues to burn out of control and has burnt close to 220,000 hectares.

But another fire has grown on its southern flank. The Clyde Mountain fire is burning on the southern side of the Kings Highway, west of Nelligen.

It was more than 3500 hectares on Monday morning and was also out of control.

On Monday and Tuesday temperatures are forecast to reach in the late-30s in parts of the fire ground with wind gusts of up to 45km/h, according to the Bureau of Meteorology forecaster Abrar Shabren.

"A high pressure system sitting over the Tasman Sea is dragging in a hot, dry air mass from central Australia over the region, across to NSW and particularly towards the southeast coast," he said.

"The Currowan fire to the east of Canberra, all of that area will actually have quite hot temperatures."

Dry thunderstorms posed a risk, Mr Shabren said. He said there would be a reprieve on Wednesday but temperatures would start to spike again on Thursday.

On Saturday night and into Sunday, crews worked on backburning operations around the north eastern parts of the Currowan fire ground, NSW Rural Fire Service district officer Brad Collins said.

"We have got some worsening weather coming through the coming days so we are conscious of introducing more fire onto the ground," he said.

An area of focus was to stop the fire from jumping the Shoalhaven River near Burrier and Bamarang but Mr Collins said they wouldn't put firefighters in harm's way to do so.

"The fire is continuing to spread in a northerly direction and that's going to be primarily our focus for now and into the coming days. We're doing as much preparation work as we can," he said.

There are separate fires burning to the north and south of the Currowan blaze. In the north, the Forest Road fire in Comberton and in the south, the Araluen Road fire in the Deua River Valley.

The Charleys Forest Fire, burning on the western flank of the Currowan blaze in the Queanbeyan-Palerang district, was at almost 35,000 hectares on Monday morning and was being controlled.

The blaze has impacted three main areas - Nerriga to Douglas Paddock, Oallen Road and Welcome Reef and in the Monga National Park east of Tudor Valley Road.

RFS public liaison officer Fiona Amundson said crews were braced for a difficult day on New Year's Eve.

"Relatively speaking, and it's sad to say, today is only very high fire danger and that's likely to increase over the coming days," she said.

"Tuesday is looking very windy and we're making plans to make sure we have enough crews and containment strategies in place before then."