A major bushfire has destroyed at least 33 homes in New South Wales and damaged an observatory, as fires continue to burn across the state.
The fire forced staff to evacuate from the Siding Spring Observatory, in the state's north-east.
But while several buildings were affected, key telescopes appeared not to have suffered "major damage".
More than 170 fires are burning in New South Wales, as lightning strikes cause more blazes amid hot and windy weather.
At least 30 fires remain uncontained, officials say.
Fires are also burning in Victoria and Tasmania, where a firefighter tackling a blaze on the Tasman peninsula was found dead on Sunday. A report on his death is being prepared.
The fires have been caused by days of searing heat across much of the country - so much so that Australia's Bureau of Meteorology was last week forced to add a new shade to its colour-coded temperature chart, for heat above 50C.
The fire, in the Coonabarabran area, had burned through nearly 40,000 hectares, Australian media reported.
"The smoke plume of that fire extended some 14km (8.6 miles) into the air and even prevented us from getting aircraft overhead because of just how dangerous and bumpy the conditions were," RFS Deputy Commissioner Rob Rogers was quoted by ABC News as saying.
The Siding Spring Observatory, located high in a remote area, is home to Australia's largest optical telescope, the 3.9m diameter Anglo-Australian Telescope, as well as several others.
Five buildings including staff accommodation and a visitors' centre had been severely affected when the fire came through on Sunday, the Australian National University, which runs the site, said in a statement.
"An initial visual assessment this morning indicated that no telescopes appear to have received major damage, but the impact of the fire on the instruments will not be known until a technical inspection of the telescopes can be done when the site is safe," it said.
Teams are on their way to assess the damage, it said.
Firefighters say at least 33 homes have been lost in addition to the damage at the observatory and that that figure is likely to change.
The fire has moved north and is still burning but the NSW rural fire service said winds had dropped, slowing its progress. Extra teams have been brought in to tackle the blaze.
Cooler temperatures are being seen in fire-hit areas after last week's peak heat, however.
Thousands of firefighters have been working to contain the blazes and residents have been evacuated from sites in all three states.
With the exception of the firefighter in Tasmania, however, no deaths have yet been reported.