Open fires are banned on Saturday in the ACT and the NSW southern ranges, southern slopes and Monaro alpine areas, with temperatures forecast to sit well above average across much of the state.

The ACT and NSW southern ranges have been deemed at "severe" fire risk while "very high" fire danger warnings are in place for eight other NSW regions, including greater Sydney and the Illawarra-Shoalhaven.

Sydney will experience a comfortable 29C maximum, but temperatures across western Sydney and on the city's fringe are likely to top 35C.

A rapidly-growing fire near Tarcutta in the Snowy Valleys was on Saturday afternoon raised to "emergency" level as it burns erratically towards the east. It has since been downgraded back to "watch and act".

"We've sent the large air tanker to assist in trying to slow the spread of that fire down, especially around the head," a Rural Fire Service spokesman said.

The large Currowan fire on the NSW south coast is also at "watch and act".

The Bureau of Meteorology, meanwhile, expects the fire danger to continue escalating into next week, with increasing heat and dry winds.

Temperatures are expected to peak on Tuesday, with New Year's Eve forecasts of more than 40C across western Sydney and in regional NSW.

The rising temperatures come after firefighters spent the past six days striving to contain large and complex bushfires before conditions worsen.

Two firefighters were killed this fire season and as many as 1000 NSW houses destroyed. Almost 110 fires were burning in NSW on Saturday.

RFS Commissioner Shane Fitzsimmons said firefighters had completed challenging work in areas such as the Blue Mountains and south coast, backburning and establishing containment lines.

Mr Fitzsimmons said the RFS was not expecting a return of catastrophic conditions, but firefighters and communities would be challenged.

Blue Mountains City Council mayor Mark Greenhill told AAP this year's extended bushfire season meant locals were living with immense stress.

The area continues to be affected by the Ruined Castle and Grose Valley fires, which spread from the Gospers Mountain mega-blaze to the north.

The Green Wattle Creek fire to the south may also pose a threat in the future, Mr Greenhill said, adding the community was "far from out of the woods".

"For the whole community this is a very stressful, long endurance episode for them; it just goes on and on," he said on Friday.

NSW Emergency Services Minister David Elliott has gone on a family holiday overseas but says he will continue to receive twice-daily RFS updates.

Frontbench colleague Anthony Roberts has stepped into the role.

Meanwhile, police have charged a 71-year-old man for allegedly lighting a fire without a permit northwest of Moruya on the NSW south coast, causing a 40-hectare bushfire in the Wandera State Forest, and charged another man for allegedly lighting two bushfires near Cessnock in the Hunter.

Australian Associated Press