"We are not aware of a link to the school and we believe these are random attacks," he said.
"We understand that students from other schools have also been assaulted.
"This is a traumatic event for the boys and their parents and the school is supporting the families at this time and working with the police."
Police said a 15-year-old has been arrested following a number of incidents at the mall, the latest occurring on Saturday.
He now faces a number of charges including aggravated robbery and assault with intent to injure.
Canterbury police inspector Viki Walker said police received multiple calls following reports of a large group of youths fighting.
"Four youths were allegedly attacked during the incident and received minor injuries.
"Additionally to this, there were two other incidents where youths were threatened and had items stolen."
Police attended the scene but were unable to find those involved.
The police were increasing their patrols in the Westfield Mall area, she said.
Halswell-Hornby community board chair Mike Mora said there was growing concern.
"Seems to me that they're just attacking people because they're young and they feel like, as a group, they need to go and attack someone to show they've got control over the area which is very disappointing and concerning."
He said a community safety meeting was being organised with reports of similar problems occurring throughout the city.
Beyond Christchurch, retailers and shoppers at malls around the country have also noted "increased anti-social behaviour".
Retail NZ chief executive Greg Harford said ongoing incidents could have an impact on businesses.
"Ultimately if customers or staff members are fearful about going into a store, they may not, they may stay away," he said.
"It can lead to a decline in sales and can make people feel really unsafe and on edge as they go to work and leave at the end of the day."
Multiple residents on Riccarton Rd (a major access route to and from Westfield Mall) who RNZ spoke to today claimed to have witnessed recent incidents of youth violence and bullying around malls in Christchurch.