A 14-year-old boy who police say may be radicalised by a “salad bar of ideologies” from the internet had reportedly threatened to carry out an alleged “Christchurch-style” attack last year.

Multiple media outlets report the teenager had planned to launch the alleged terror attack at a Sydney school in September and was charged over the plans.

However, charges were dropped in the Surry Children’s Court on mental health grounds in February this year and the boy was placed in a government deradicalisation program, reports The Daily Telegraph.

The teen, dressed from head to toe in camouflage gear and carrying a black backpack, was arrested on Tuesday after he allegedly stabbed a 22-year-old university student in the neck with a kitchen knife.

Counter-terrorism police were called in after the incident at the University of Sydney around 8.30am on Tuesday, at the inner-city Camperdown campus.

The victim was rushed to Royal Prince Alfred Hospital but was in a stable condition late on Tuesday.

CCTV vision shows the teenager after the alleged attack, clutching his own bloodied and injured hand while walking along Missenden Road.

He reportedly caught a public bus to the Royal Prince Alfred Hospital.

Police ruled out religion as a motivating factor behind the attack, instead blaming the ability to access extreme violent content online as what allegedly radicalised the teen.

The Daily Telegraph reports he allegedly had a close interest in controversial commentator Andrew Tate.

NSW Police Assistant Commissioner Mark Walton said the teen’s ideology would likely be classed as “mixed and unclear”, as he put it: “the salad bar of ideologies”.

“A lot of these vulnerable people, they’re not linked to one particular ideology, they will move as they’re exposed to different things,” he said on Tuesday.

“It might be of white supremacist neo-Nazi, it can easily flip into a religious ideation, it’s a very complex environment that some of these vulnerable people are engaged in, not a linear position.”

The 14-year-old was arrested after he attended the same hospital, where he was treated for cuts and undertook a mental health assessment.

He was known to police and government agencies, Mr Walton 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.

-with AAP