The Currowan fire, on the South Coast, will continue to burn until there is substantial rain on the fireground, according to the NSW Rural Fire Service.
The bushfire was at "advice" level on Sunday afternoon, but was out of control. It had burnt out more than 77,000 hectares.
It remained active in areas north of the Kings Highway and in the areas of Benandarah, Windywoppa and Currowan.
The fire could flare up in Lake Tabourie, Bawley Point, Kioloa, Pretty Beach, Pebbly Beach, Depot Beach, Durras North and South Durras.
NSW Rural Fire Service operational officer Bradley Stewart said crews were prepared for a "protracted campaign" to fight the fire.
"The fire will be here for some time to come, fundamentally this fire won't be out until it's had very good rain," he said.
"We'll be able to contain it, we'll be able to put it in a box but areas of it will be on fire until all of that material that's alight burns out or we get substantial rain."
On Sunday, crews were conducting back burning operations off the Kings Highway, east and west of Nelligen, Mongarlowe, around the area of Woodburn and the Western Distributor Road.
Conditions were more favourable to crews on Sunday but it is forecast to deteriorate by Tuesday.
Mr Stewart said while there was a forecast for elevated fire conditions it was a bit far out to get a firm indication of what that would mean for the fire.
The Princes Highway remained closed between Burrill Lake and the Kings Highway turnoff and the Kings Highway is closed between Nelligen and Forest River Road, Monga.
"Roads and Maritime Services have got a number of work crews committed to reopening the Princes Highway as soon as it's practical to do so," said Mr Stewart.
"There has been some substantial damage done to road infrastructure, including some culverts that may or may not need to be replaced and are waiting on the engineers to make their assessments. We can't give a timeline on that but we are hoping in the next several days."
More than 200 firefighters battle the blaze on a daily basis, Mr Stewart said. Crews from the National Parks, Forest Corporation, Fire and Rescue NSW, Fire Rescue Victoria and the NSW State Emergency Service are currently fighting the fire.