Horror conditions expected on Thursday will increase the risk the North Black Range fire could escape containment lines and impact properties.
There is a severe fire danger warning and a total fire ban in place for Braidwood and the surrounding area.
The ACT will also have a total fire ban on Thursday.
NSW Rural Fire Service Lake George District officer Darren Marks said the area to south-east of the fire, at Wallaces Gap, was of most concern.
"We're backburning the south-east area of the fire to endeavour to prevent it pushing out of Tallaganda into the Wallaces Gap area and beyond," Mr Marks said.
He said while firefighters were taking action on Wednesday night to prevent the spread of fire, the RFS could not guarantee the fire would not reach into Wallaces Gap.
If the fire did spread, Majors Creek and the immediate surrounding area would be most at risk.
Mr Marks said residents in this area that did not have a bushfire survival plan or their plan was to leave then they should leave by 8am on Thursday.
There is an evacuation centre set up at the Braidwood National Theatre which would be open from 11am.
Braidwood is not expected to be threatened by fire on Thursday, but the conditions were expected to be similar to Friday's which saw the fire make a run towards Braidwood.
"[Thursday] is going to be an extremely challenging day and we want people living in or near the fire affected area to be on maximum alert," Mr Marks said.
The area to the north-west of Braidwood, around Colombo Road was another area of concern for the RFS, Mr Marks said, which could see the Kings Highway or Cooma Road closed with no notice.
Mr Marks said he did not envisage the North Black Range fire and the Currowan fire, currently devastating the south coast, joining up tomorrow.
The fires are currently about 20 to 25 kilometres apart and Mr Marks said in worst case scenario the fire was expected to extend 10 to 15 kilometres on Thursday.
There will be a reprieve of sorts for firefighters battling the blaze after Thursday, but that may not last long.
"If it holds [on Thursday] it will be a good sign for the days to come," Mr Marks said.
However, he indicated the RFS did not expect the fire to be contained by Tuesday.
Canberrans planning to head to the coast over the weekend are encouraged to reconsider if any trips are necessary.
The North Black Range fire could close the Kings Highway and the Princes Highway is closed north of Batemans Bay. Mr Marks said anyone travelling to the coast may find it difficult to get back.
Braidwood is expecting a top of 27 degrees on Thursday and winds could reach 55km/h in the morning before decreasing in the evening.