ASIO director-general Mike Burgess says Australia's terror-level threat has been raised to "probable" due to a rising mix of ideologies where more people think "violence is permissible".

Mr Burgess had earlier on Monday joined Prime Minister Anthony Albanese and Attorney-General Mark Dreyfus in making the announcement, where he said eight incidents had been disrupted in the past four months.

The raising of the threat level does not mean ASIO has intelligence about plans of an imminent attack.

Speaking to 7.30, Mr Burgess said not one of the eight incidents in isolation caused the raising of the threat level.

In six of the eight cases identified by the intelligence service boss the individuals involved were previously unknown to police or ASIO.

"One incident or a couple of incidents are not a reason to raise the threat level, but they are an indication of what we're seeing in society across those eight incidents," Mr Burgess said.

"Five of them involved minors or youth. The oldest was 21. The youngest was 14. 

"Across the eight there's an equal mix of religiously motivated, nationalist and racist violent extremism."

Mr Albanese earlier said the raised level had been driven by increases in youth radicalisation, online radicalisation and the rise of "new mixed ideologies".

The sheer range of threats and the speed of evolution from idea to action means that ASIO is stretched in its role of keeping Australia safe.

Mr Burgess said mixed ideologies lacked logic but were often based on violence.

Asked if the eight incidents he referred to were mostly religiously motivated, Mr Burgess said the total number was less than half.

He said the agency observed that violence was becoming more permissible, with religiously motivated, nationalist or racist ideologies sometimes becoming mixed in ways that do not make sense.

"[In] one particular incident, we have an individual that's latched onto ANTIFA, so extreme left wing, but actually in the manifesto, there's neo-Nazis … that defies logic," he said. 

Mr Burgess then added that those incidents — which all came after the Wakeley stabbing, where the perpetrator was charged with a terror offence — involved people who were unknown to police and been prepared to act quickly.

"This is the new thing, people will go to violence with little or no warning, and they [have] little or no planning in some of these that I've talked about," he said.

Young Australians are vulnerable

Mr Burgess said young Australians in particular were being targeted, especially online.

"The youth are particularly vulnerable," he said.

"The internet is a great thing but it also allows individuals to catch on to something and get there in a matter of days, not months or years, and that's particularly concerning now."

Mr Burgess said the trend started during the pandemic, when people were locked down, but it had continued since and a stretched ASIO had tried to combat it.

"COVID is no longer with us, but it's a concern how social media can grab people quickly. The internet can grab people quickly and hurt young brains which are not fully formed."

'Terrorgram and accelerationists'

Asked what other ideologies were in the mix, Mr Burgess said neo-Nazism remained a prominent area but even though it had dropped off he was concerned with "accelerationists".

He defined that group as those with a far-right ideology who "believe in white supremacy and don't like the way the world is run today, and want its downfall".