A Northland High School was put into lockdown for an hour after fighting broke out and parents went onto school grounds.
Police were called to Kaitāia College at about 1.30pm on Wednesday in response to a report of a person trespassing on the school grounds, a police spokesperson said.
At 2pm, a message posted on social media from the school said the college was in lockdown and urged parents not to come to the school or phone in.
"This may cause disruption to the management of this incident and could potentially place yourselves and our staff and student's safety at risk," the post said.
Shortly before 3pm, the school came out of lockdown and the college confirmed all students, staff and people who were on-site had been safely accounted for.
"Everyone did extremely well and responded to instructions."
It said parents and caregivers of students would be given a notice on Wednesday evening to provide more information on what happened at the school.
"Officers are no longer present - the person trespassing left prior to police arrival," Police have said.
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