Teenage boy arrested by Australia police after stabbing at Sydney university

NSW Police Asst. Commissioner Mark Walton says boy's motive unknown, warns of youth radicalization online.

Australian police said it had arrested a 14-year-old boy after a stabbing at the University of Sydney on Tuesday morning, which triggered a lockdown of the university buildings.

Emergency crews treated a 22-year-old man, who was taken to a hospital in a serious but stable condition, New South Wales state police said in a statement.

New South Wales Police Assistant Commissioner of counter terrorism Mark Walton told a news conference the boy's motive or ideology had not yet been determined, but expressed concern at increasing evidence young people were being radicalised online.

"They are embracing violent extremist ideologies and moving towards violence," he said.

The attacker was known to police and government agencies, he added.

The alleged attacker boarded a bus after the incident and was arrested near a hospital, police said. There is no ongoing risk to the community, and the victim and the alleged attacker were not known to each other.

A University of Sydney spokesperson said a police operation was underway at its Camperdown campus and that police would remain on campus while investigations continue.

Police have cordoned off the crime scene.

The attack comes about two months after six people were killed and 12 injured in a knife attack at a mall in Sydney's Bondi area, and an Assyrian church bishop was wounded in an unrelated stabbing attack during a service in Sydney's west.

A 16-year-old boy was charged with a terrorism offence over the stabbing of the bishop, while the attacker at the mall was shot dead by police.

The two attacks had prompted the New South Wales state government to toughen its knife laws. The state parliament passed laws in June giving police electronic metal-detecting scanners to check people without a warrant at shopping centres, sporting venues and public transport stations.

The law also raised the maximum penalty for selling a knife to a child under the age of 16 to A$11,000 ($7,314), imprisonment for 12 months, or both. It also prohibited selling a knife to a child aged 16 or 17 without a reasonable excuse.