Australia's only nuclear reactor, at Lucas Heights, halted production of the radioisotope known as molybdenum-99 (Mo-99) after a mechanical fault at the facility on September 6.

Mo-99 is used in 85 per cent of nuclear medicine scans to diagnose cancer, heart disease and other abnormalities.

It's also needed to produce Technetium-99m, a radioactive tracer which is injected in patients to diagnose a variety of health conditions including heart, lung, organ and muscular-skeletal conditions.

An Illawarra Shoalhaven Local Health District spokesperson said the shortage was impacting nuclear medicine services across Australia, and it was not known when the stock levels would return to normal.

"The Ministry of Health is participating in a national working group to determine allocation of available stocks of technetium-99m as equitably as possible," the spokesperson said.

"The Ministry of Health has also provided guidance to local health districts on actions to limit the impact of the shortage.

"These include considering alternative diagnostic modalities where clinically suitable."

Alternative tests may include positron emission tomography (PET) scans, however there are some circumstances where alternative tests cannot be done.

Associate Professor Barry Elison, director of the nuclear medicine department at Wollongong Hospital, said the region's hospitals and medical imaging centres had been prioritising scans for patients who needed them most.

"Generally speaking when there's a shortage, the hospitals and clinics are very good at prioritising urgent cases," he said. "However elective cases may be delayed a week or so, which doesn't impact on their management."

Prof Elison said stocks of the isotope had been quite stretched in mid-September but had since been boosted by supplies from overseas.

"During national shortages, Australia usually sources nuclear isotopes from South Africa," he said. "However in September the South African reactor was undergoing maintenance so supply was affected quite badly.

"But the supply of medicine is now increasing from overseas and we should be back to full supply in coming weeks."

However it is not known when production will resume at the Australian Nuclear Science and Technology Organisation's Lucas Heights facility.

"ANSTO is currently importing bulk Mo-99 from international manufacturers which is then being processed and placed into generators at Lucas Heights for safe local distribution," an ANSTO spokesperson said.

"A nuclear medicine working group, which comprises key groups within the nuclear medicine community, has been providing advice to ANSTO on how to distribute supplies most equitably.

"Local manufacturing of bulk Mo-99 will resume after the fault is safely and properly rectified."

The spokesperson said ANSTO was working closely with the nuclear medicine community to keep them informed on progress.

Meantime the Australian Government has added six temporary item substitute tests to the Medicare Benefits Schedule to enable broader access to nuclear medicine scans using alternative tests.

This will minimise out-of-pocket costs to patients and increase access to other scans during the shortage.