AFTER "a hell of a week", NSW's bushfire crisis is not over yet, the state's acting premier says.

A fire in Warrumbungle National Park, west of Coonabarabran in the central west, destroyed at least 33 homes and damaged the Siding Spring Observatory on Monday.

Fifty farm sheds were also lost along with many livestock, much fencing and farm machinery.

It is one of 146 blazes across the state that are testing almost 800 firefighters.

The Warrumbungle fire burnt through 40,000 hectares after beginning its destructive rampage on Sunday.

On Monday it still had a 100km front, although no further properties were immediately under threat.

Rural Fire Service (RFS) Deputy Commissioner Rob Rogers said a wind shift at the worst possible time had created "perfect storm" conditions for a fire that burnt with a ferocity not seen in years.

"There was just absolutely no stopping that fire," he said.

Acting Premier Andrew Stoner said while a subsequent wind change had removed the threat to the town of Coonabarabran it could threaten settlements to the north of the national park.

More than 110 people were evacuated to the Tattersalls Hotel in Baradine and a relocation centre was established at the Coonabarabran Bowling Club, with residents warned it was not safe to return home.

Mr Stoner said it was "miraculous" the main building and Australia's largest telescope at the Siding Spring Observatory were not destroyed although the Australian National University (ANU) facility was damaged in the fire.

ANU Acting Vice-Chancellor Erik Lithander said the observatory will be closed for two weeks while a full assessment is undertaken.

Dr Lithander said 18 staff were evacuated from the site on Sunday afternoon and while they were safe, there were fears some had lost their nearby homes in the blaze.

At least five buildings at the observatory had been damaged significantly, including the lodge used to accommodate visitors at the site, the visitor's centre, a number of residential cottages used by staff and a number of sheds.

"An initial visual assessment shows that there does not seem to be significant damage to the buildings that house the telescopes," Dr Lithander told reporters in Canberra.

"We do not yet know what impact the extreme heat or the ash might have on the telescopes themselves and we won't be able to carry out that assessment until we can enter the buildings and inspect the inside of them."

While easing conditions had helped stop the fire spreading, the RFS said additional crews were being deployed to the area ahead of deteriorating weather conditions later in the week.

On Monday, more than 770 firefighters, 208 trucks and 78 aircraft were deployed to tackle the 146 fires, 36 of which are not contained and 13 which are out of control.

So far the fires have scorched more than 500,000 hectares of bush and grassland - the equivalent of the entire greater Sydney basin, RFS spokeswoman Laura Ryan told AAP.

Western NSW Minister Kevin Humphries on Monday visited RFS headquarters in Narrabri, where he was briefed on the situation and thanked SES and RFS volunteers.

"I have had the chance to meet with many of them today, and I was awestruck by their commitment to battling these blazes despite being overcome by heat and exhaustion," Mr Humphries said in a statement.

"The incredible response to save the world-famous Siding Spring Observatory from being completely destroyed is an absolute credit to all involved."

Much work was still needed to contain the fires burning throughout the region, Mr Humphries said.

"With high temperatures set to continue throughout the week the crisis is far from over," he said.