Australians have been told to be vigilant but continue their way of life as the nation's terrorism threat level is lifted for the first time in a decade.
The threat level has been raised from "possible" to "probable" because of an increased risk of politically motivated violence.
The heightened risk didn't stem from one incident, intelligence agency ASIO said, as it revealed eight attacks or disruptions that involved alleged terrorism had been investigated in the past four months.
ASIO chief Mike Burgess stressed the upgrade to probable didn't mean inevitable.
"Australians should be aware but not afraid," Mr Burgess told reporters in Canberra on Monday.
Probable is the third-highest threat level on the federal government's advisory scale and means there is a greater than 50 per cent chance of an onshore attack being planned in the next 12 months.
ASIO dropped the terror threat to possible in late 2022.
The eight alleged incidents couldn't be detailed but underscored the threat coming from lone actors or small groups accessing "rudimentary weapons" such as knives, improvised explosives guns, Mr Burgess said.
"The threats are becoming harder to predict and identify," he said.
The threat predominantly came from young people radicalised online and radicialisation was being accelerated, with violence used "with little or no warning and little or no planning", he said.
Of the eight cases, the youngest alleged perpetrator was 14 years old and the oldest 21.
This showed "a resurgence in the number of minors embracing violent extremism," the ASIO chief said.
"Extremist ideologies, conspiracies, misinformation, are flourishing in the online ecosystem and young Australians are particularly vulnerable."
It's the first time the terror level has been raised since 2014 during the height of threats from terrorist group Islamic State.
Two dozen attacks had successfully been disrupted since then, Mr Burgess said.
Conflict in the Middle East has contributed to the revised assessment this time because it exacerbated security concerns about politically motivated violence.
But it wasn't the direct driver of the increase with none of the alleged terrorist plots investigated inspired by Gaza, Mr Burgess said.
"Terrorist leaders offshore are not inspiring attacks onshore, this is why we did not raise the threat level in the immediate aftermath of 7 October," he said in reference to the outbreak of conflict in Gaza between Hamas and Israel.
"Indirectly though, there have been important and relevant impacts, the conflict has fuelled grievances, promoted protest, exacerbated division, undermined social cohesion and elevated intolerance."
Anti-authority beliefs were also growing, along with a decline in trust in democratic institutions, Mr Burgess said.
Social media continued to push extremist views on young people by reinforcing prejudices, Prime Minister Anthony Albanese said as he called for the heat to be taken out of political debates.
"One of the things about social media is that the algorithms push people towards more extremes and they reinforce views," he said.
Opposition home affairs spokesman James Paterson described the increase "sobering but unsurprising given recent events".
Among the eight incidents ASIO viewed as terror-related was the Wakeley church stabbing in April, where two Christian clerics were injured in a stabbing attack during a service in suburban Sydney.
A 16-year-old boy was charged with a terrorism offence.
