Police are urging parents to monitor their kids' online behaviour after a teenage boy dressed in camouflage allegedly attacked a university student with a kitchen knife.
Counter-terrorism police have been brought in to investigate the stabbing at the University of Sydney, but have not identified a particular ideology and had ruled out religion as a factor.
The boy allegedly stabbed a 22-year-old man in the neck at the inner-city Camperdown campus about 8.30am on Tuesday with paramedics treating him at the scene before rushing him to Royal Prince Alfred Hospital.
The campus went into lockdown as police raced to the scene and searched for the attacker.
The 14-year-old, who is from Sydney's inner-west, is alleged to have caught a bus to Royal Prince Alfred Hospital where he was arrested.
NSW Police Assistant Commissioner Mark Walton said the stabbing was being treated as a terrorist incident.
He said the boy's ideologies would likely be classified as "mixed and unclear", viewed more a cocktail of things he had likely consumed on the internet.
"There are concerns about youth being radicalised in the online environment, they are embracing violent extremist ideologies and moving towards violence," he said.
"I urge parents to be aware of this risk to their children … over the last five years we've seen the cohort of young people aged 12 to 16 really emerge in counter-terrorism investigations."
The 14-year-old boy was known to police and government agencies, Mr Walton said.
The boy was treated for cuts at the hospital and was undergoing a mental health assessment.
Police said the victim was in a stable but serious condition.
Forensic officers have been scouring the campus grounds looking for the weapon and other evidence.
In an email to staff and students, vice-chancellor Mark Scott said he was shocked and saddened by the attack on a member of the university community in what he described as an isolated incident.
"NSW Police have arrested the alleged attacker and have assured us that there is no ongoing threat to the community," he said.
A university spokeswoman said staff were working with authorities and there might be an increased security and police presence on campus while investigations continued.
Students were notified a number of buildings at the university had been placed in "secure mode" and would require swipe cards for access.
University international cardiology fellow Matheus Silva said he was concerned by news of the stabbing after moving away from his home country to escape violence.
"One of the main reasons I left Brazil was because of the criminality," he told AAP.
