The North Black Range bushfire has been upgraded as firefighters battle worsening conditions.
The fire was upgraded from advice level to "watch and act" about 2.30pm on Tuesday
It comes as new spot fires have broken out in areas of the bushfire near Braidwood as strong winds and hot temperatures challenge fire crews.
The spot fires have been seen to the north of the fireground near Foxs Elbow and Butmaroo. Hot spots have also popped up near Forbes Creek, which had been inactive for several days.
The North Black Range fire is now just 20 kilometres away from the Currowan fire, which has ravaged a large part of the South Coast.
Residents near Mongarlowe have now been told to monitor conditions of the Currowan fire as that fire shifts west.
On Tuesday at 2.30pm, the North Black Range fire had burnt more than 35,000 hectares. The fire remains active near Jones Road, Watsons Road and Mulloon Creek. It's also pushing up into areas along Manar Road.
A total fire ban has been declared for the Southern Ranges and the fire danger rating for Tuesday has been forecast as severe.
NSW Rural Fire Service Lake George District officer Darren Marks said crews were keeping on top of spot fires that broke out across the fireground.
"We're expecting a challenging afternoon, potentially up until about 6pm," Mr Marks said.
"The northern area is where we have the most active fires at the moment and that's the principle concern."
Strong winds, temperatures in the high 30s and low humidity are likely to hamper firefighting efforts on Tuesday.
A south-easterly change forecast for Tuesday evening is expected to bring some relief for crews on the ground.
"Tuesday will be the worst of the conditions for this week," Mr Marks said.
"It looks like we'll be getting very different conditions between the coast and the inland areas and the size of the fireground means we could have considerably different conditions going forward."
Crews have been working to strengthen containment lines around the fire.
"At this stage, no properties are under threat and the fire is burning in heavy scrub areas," Mr Marks said.
"The message is around the fireground on Tuesday is for residents to maintain their vigilance."
An ACT fire truck was damaged by a fallen tree while it was being used to help fight the bushfire.
An ACT Emergency Services Agency spokesman said fire crews who were using the truck in firefighting efforts were away from the truck at the time.
No injuries have been reported and support is being provided to fire crews.
The truck was one of 80 vehicles being used as part of firefighting efforts for the bushfire.
The spokesman said the truck was being assessed and repaired and would return the fireground as soon as possible.
"This is a timely reminder for the community to be mindful of the dangers of falling trees when travelling in or around fire areas," the spokesman said,
"We are so thankful our team is OK."