Overall, Australia's security environment is becoming "degraded", Mike Burgess said in a wide-ranging speech that declassified some of his agency's secretive thinking about the national threat outlook.

Besides disclosing the international subterfuge waged against Australia, Burgess cautioned that terrorism remained a real threat but that the perpetrators were now more likely to be acting alone, and in their teens.

Australian plans to deploy stealthy nuclear-powered submarines in a pact with the United States and Britain -- known as AUKUS -- offer an enticing target, including to friendly nations, said the Australian Security Intelligence Organisation (ASIO) director-general.

Foreign intelligence services seek to understand future AUKUS submarines' capabilities, how they will be deployed, and to undermine allies' trust in Australia, Burgess said in the speech in Canberra.

By 2030, they are more likely to focus on interference to undermine support for AUKUS and "potentially sabotage" if regional tensions escalate, he said.

Australian defence personnel were being "relentlessly" targeted.

"Some were recently given gifts by international counterparts. The presents contained concealed surveillance devices," Burgess said.

Australia was not immune from hostile states like Iran undertaking "acts of security concern" on its shores.

"ASIO investigations have identified at least three different countries plotting to physically harm people living in Australia," Burgess said.

"In a small number of cases, we held grave fears for the life of the person being targeted."

In one case foiled by ASIO, a foreign intelligence service planned to silence an Australia-based human rights activist by luring the person abroad and staging an accident to seriously injure or kill the target, he said.

Last year, a different hostile spy service sought to "harm and possibly kill" one or more people on Australian soil as part of a broader effort to eliminate critics, Burgess said.

This effort, too, was thwarted by ASIO.

In both cases the plotters were overseas, but those involved know "how we will deal with their agents", he said.

- 'Major terrorism plots' thwarted -

Multiple foreign governments "continually" attempted to coerce Australian citizens and residents to report on fellow members of the same diaspora.

At least four countries had tried to pressure individuals to return to their countries of birth, including in one case by seizing assets and threatening the victim's family, friends and former classmates.

Burgess said the country's counter-terrorism defences were robust, and his service along with law enforcement had disrupted "dozens of major terrorism plots" including five last year.

Of all the potential terrorism plots investigated last year, fewer than half were religiously motivated, while most involved "mixed", nationalist or racist ideologies.

"Almost all the matters involved minors. All were lone actors or small groups. Almost all the individuals were unknown to ASIO or the police," the intelligence chief said.

The median age at which minors are first investigated by ASIO is now 15. Eighty-five percent of them are male. And they are overwhelmingly Australian-born, Burgess said.

Looking ahead, a new generation would become potential targets for online radicalisation.

"If technology continues its current trajectory, it will be easier to find extremist material, and AI-fuelled algorithms will make it easier for extremist material to find vulnerable adolescent minds."

Australia's national terrorism threat level was raised last year to "probable", Burgess noted.

"I do not anticipate being able to lower it in the foreseeable future."