Firefighters say they are confident they can stop a bushfire in southern New South Wales from reaching a former military range scattered with unexploded bombs.

The Deans Gap bushfire, one of more than 100 fires burning across the state, is out of control near Wandandian.

Fires are , after record temperatures earlier this week.

Just a few kilometres from the Dean's Gap blaze is the Tianjara plateau, which was used by the Army as a practice bombing range for 30 years until the mid-1970s.

It is now part of the Morton National Park, but unexploded ordnance remains scattered throughout the range.

Brett Loughlin from the Rural Fire Service (RFS) says unexploded bombs would make it impossible to fight a fire.

"We can't do any water-bombing with aircraft or something like that in case the weight of the water when it hits the ground sets off any unexploded ordnance," he said.

"So it's a total no-fly zone and that will mean [if] the fire gets into that area, there's nothing we can do for it except wait for it on the other side.

"So that could compound our firefighting strategies."

Mr Loughlin said crews have used a special gel and bulldozing containment lines to stop the fire from entering the range.

The Deans Gap fire has consumed around 6,000 hectares of bushland.

A large fire that burned to within 11 kilometres Yass has now been brought under control but farmers now face the grim task of destroying thousands of burnt animals.

There is also concern for a fire at Cooma.

Firefighters around the nation have taken advantage of cooler conditions today to bolster containment lines ahead of high temperatures and unpredictable winds tomorrow.

A total fire ban has been issued for the the whole of New South Wales, the ACT and Victoria, while fire bans also cover much of South Australia.

Authorities in Victoria are warning that the conditions mean any fires will move quickly and become out of control in a short time.

Tasmanian fire crews are making progress in building containment lines around the state's most damaging bushfire on the Forestier Peninsula.

Authorities hope to reopen the Arthur Highway tomorrow allowing residents to return to Dunalley, where homes and businesses were destroyed by fire a week ago.