Australia's largest telescope, along with a suite of smaller telescopes, has narrowly escaped being taken out by bushfires which razed buildings at an observatory in northern NSW.

The Siding Spring Observatory will be closed for two weeks while the impact of the fires is assessed, Australian National University (ANU) Acting Vice Chancellor Erik Lithander said.

Dr Lithander said 18 staff were evacuated from the observatory on Sunday when a fire in the neighbouring Warrumbungle National Park of northern NSW burnt through 40,000 hectares.

The fire destroyed at least 15 properties after a sudden wind change.

Dr Lithander said there were fears some staff had lost their homes in the blaze.

At least five buildings at the observatory had significant damage, including the lodge used to accommodate visiting researchers, the visitors centre, residential cottages and 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 on Monday.

"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."

ANU staff will assess the damage, help with the clean-up and restore services when it is safe to do so.

An additional team including the ANU's chancellor and a counsellor will head there on Wednesday.

ANU acting director of facilities and services Wayne Ford said the observatory's water supply was cut after pumping stations along the main waterfeed were affected by the fires.

Electricity was also cut, but generators are providing power for essential services.

Mr Ford said the biggest challenge was to keep up a supply of diesel for the generators.

Both roads to the observatory are closed and unlikely to be opened for days.

"There's been a significant amount of trees and telephone poles that have come down," he said.

The observatory is home to Australia's largest telescope, which helps researchers unlock the secrets of the universe.

Astronomy and astrophysics research school acting director John Morris said the telescope had undoubtedly attracted Nobel laureate Brian Schmidt to Australia.

"He spent a lot of time at Siding Spring, and he's been watching what's been going on with great interest," Prof Morris told reporters.

Prof Morris said they could still communicate with the telescopes at the observatory, but it would take some time to see if embers and extreme heat had damaged the equipment.

He said it was a close shave, with the main telescope just a two-minute walk from the visiting researchers' lodge that was burnt.

The university has organised an appeal to support staff whose homes may have been lost.

One of the last people to flee the observatory before the fire swept through the area says scientists will return soon, but may have to camp out at first.

"It is summer, so that wouldn't be too bad," University of Queensland astrophysicist David Parkinson said on Monday.

"In terms of science, we'll be back fairly soon."

Dr Parkinson, who was working at the observatory over the weekend, said he and five other scientists could see a bushfire burning in the Warrumbungle National Park on Saturday, but they thought they would stay put because it looked small.

"We didn't see it as a threat. It was just something to look at," he told AAP.

But when the scientists woke up on Sunday there was a lot more smoke and the fire was much closer.

At 3.30pm (AEDT) Dr Parkinson and his colleagues got the call to leave.

"We all just jumped in the cars and drove. The drive down the mountain was a little hair-raising because we knew the other side of it was already on fire," he said.

After looking at pictures and video of the site after the fire swept through, Dr Parkinson said it's only now becoming clear how close they might have been to danger.

"Some telescopes survived, but the lodge where we were staying is flattened," he said.

"It will have to be built again from scratch."