A public health expert has urged people to get tested and vaccinated as diphtheria spreads from the Northern Territory to Western Australia, Queensland and South Australia.

The outbreak, which has overwhelmingly impacted Aboriginal communities has caused at least one death, the Central Australian Aboriginal Congress reported last week.

The strain of respiratory diphtheria can be deadly if left untreated, however diphtheria is a vaccine-preventable disease and had last caused a death in Australia almost ten years ago.

The Territory's Health Department declared an outbreak of the disease in March, the first diphtheria outbreak in Australia for about three decades.

There have been more than 161 confirmed cases. Australian Centre for Disease Control data indicates the vast majority of locally acquired cases are residents in "outer regional", remote or very remote areas and more than 98 per cent of cases are Indigenous.

Dr Milena Dalton, the head of Immunisation and Health Systems Strengthening at Burnet Institute, said on Tuesday that reports the outbreak has spread into Western Australia, Queensland and South Australia are "deeply concerning".

"This is no longer an isolated outbreak and it highlights how quickly vaccine-preventable diseases can re-emerge when there are immunity gaps," she said.

"Diphtheria remains rare in Australia because vaccination works. But this outbreak is a reminder that rare does not mean impossible, and that protection needs to be maintained through timely boosters for adolescents and adults.

"The most important message is that diphtheria is preventable. Vaccination and boosters remain our best protection against severe disease, hospitalisation and death, and they are especially urgent in communities where people face barriers to healthcare."

Dr Dalton said the fact the outbreak is affecting Aboriginal communities "points to the need for a rapid and culturally safe public health response".

"That means working with Aboriginal community-controlled health services, trusted local leaders and frontline workers to make testing, treatment and vaccination as accessible as possible," she said.

"Getting tested, treated and vaccinated protects individuals, families and the wider community."

Central Australian Aboriginal Congress chief medical officer of public health, Dr John Boffa, said on Friday that federal resources are needed now to deliver vaccinations and booster shots to stem the spread of the disease.

Dr Boffa told the ABC the disease was spreading across the Territory, with current case numbers of respiratory diphtheria and cutaneous diphtheria surpassing 100 and a number of people being admitted to intensive care.

He said the majority of the people becoming "seriously sick" after contracting diphtheria were either unvaccinated or had not received a booster in the recommended time frame.

The death in 2018, the last recorded before this outbreak, involved an unvaccinated adult.

A spokesperson from the federal Department of Health, Disability and Ageing told the ABC the federal government has been working with the NT government, the Australian Health Protection Committee, and the Aboriginal community controlled health sector on "a range of measures to support the response to Diphtheria in the NT".