Smoke damaged some buildings housing telescopes at Australia's top astronomy research observatory, but fire-proofing work prevented "catastrophic" damage from a weekend inferno, officials said Tuesday.

The mountaintop Siding Spring Observatory, about 500 kilometres (330 miles) northwest of Sydney, was engulfed by flames during the firestorm on Sunday evening which razed 33 nearby homes and some of the facility's outer buildings.

Eighteen staff working at the Aus$100 million (US$105 million) observatory -- which houses 10 telescopes run by Australian, Polish, British, South Korean and US researchers -- were safely evacuated before the fire struck.

The Australian National University, which administers the observatory in the remote Warrumbungle Ranges, said it had confirmed Tuesday that three buildings -- two lodgings and a storage unit -- had been destroyed by the fire.

Another three buildings including the site's visitors' centre had been badly damaged by the flames, but the university said initial assessments suggested that the telescopes themselves had dodged the worst.

"Four telescopes appear to have some smoke damage to their buildings (but) fire preparation works appear to have been successful in preventing catastrophic damage to the scientific facilities," it said.

Siding Spring is Australia's top optical and infrared observatory site and plays a key role in Southern Hemisphere astronomy research.

The main Anglo-Australian Telescope is instrumental in exploring the Milky Way and Magellanic Clouds.

The university said access was still "very limited due to safety issues" and the focus was on securing the site so that "further assessment of the scope of damage" could be made. No astronomical data was thought to have been lost.

The entire site will be shut for at least two weeks while recovery work is done. The university said a number of staff members had lost their homes in the 40,000-hectare (98,840-acre) blaze, which has since moved north.

It is the worst of 120 wildfires currently burning across New South Wales, Australia's most populous state, following a series of hot and dry days that have been followed by lightning storms.

Some 20 aircraft and 185 firefighters are working to contain the blaze ahead of a forecast return to extreme heat on Friday when the mercury is tipped to hit 42 degrees Celsius (108 Fahrenheit) in parts of the state.

"We're expecting a return to some pretty severe fire danger," a weather bureau spokesman said.

In the southern state of Tasmania, more than 100 homes were destroyed by fire earlier this month.