A lockdown at Kerikeri High was triggered when a family member of a brand-new student allegedly turned up at the school with a kitchen knife and assaulted another student.
Police say the knife was not used but appeared to have been dropped during the melee.
The drama began around 11.20am on Monday when an altercation broke out on the school grounds.
Senior Sergeant Peter Robinson, of Far North Police, said a student reportedly made threats to another group of students before leaving the school and returning with a male who did not attend the school.
The student and the male then allegedly assaulted another student, Robinson said.
''During this assault a knife has fallen on the ground. At this stage, there's no evidence to suggest it was brandished. The pair have left the school a short time later.''
Robinson said the victim was not badly injured and did not require medical assistance.
The school briefly went into lockdown while police carried out inquiries in the area.
The student involved in the alleged assault was quickly located at a property on nearby Cobham Rd. As of yesterday afternoon police were still looking for the other male.
Robinson said officers were speaking to the victim, witnesses and the students involved to establish exactly what had taken place.
''We're working closely with the school on this matter to ensure the safety of all in the school,'' he said.
In an email to parents deputy principal Mike Clent said older family members of a youth who started his first day at Kerikeri High on Monday had come onto the school grounds where they allegedly assaulted one student and threatened another with a weapon.
Clent said the incident had caused huge concern in the school and wider community.
He acknowledged the lockdown — the first at Kerikeri High — was unsettling and upsetting for parents and whānau as well as students and staff.
There appeared to be no underlying reason for the incident which the school, and police, believed had occurred ''out of the blue''.
Clent said there was no basis to speculation in another media outlet that the incident was linked to students being dropped off at the school ball last weekend by family members riding motorbikes.
He thanked ''outstanding'' staff who responded quickly and put themselves in harm's way to protect students and de-escalate the situation, and students for responding calmly and quickly.
Guidance counsellors were available for anyone upset or anxious about the day's events.
One student who contacted the Advocate, with his parents' permission, said he heard ''yelling and screaming'' as he was walking to class then saw three or four ''adult-size'' students fighting.
It was soon noticed by teachers and deputy principals who weren't afraid to get in the thick of it and break up the fight.
''One or two of the students showed aggression to the teachers, and got up in the teachers' faces threatening to hit them until a teacher with significantly larger stature than anyone else came in and stopped the fighting,'' he said.
He saw a teacher confiscate a kitchen knife, with a blade about 16cm long, and lead one of the students involved to the nearby student centre.
Five minutes later he heard a pre-recorded message that the school was going into lockdown.
His class spent the next 25-30 minutes under their desks, until the fire alarm sounded and the whole school was evacuated onto the sports field.
The first email sent to parents, at 11.31am, said the school was in lockdown due to an incident on the grounds, and that steps had been taken to ensure the safety of students and staff.
The email urged parents not to try to contact their children during the lockdown and that staff had advised students to turn mobile devices off.
''We also ask parents, whānau and caregivers to not attempt to enter the school during the lockdown,'' the message continued.
A follow-up email, at 12.14pm, said the lockdown had been lifted and students were being evacuated onto the main field for a roll call.
Parents who wished to do so could pick up their children from 12.30pm.
Kerikeri Primary School, which is directly across Hone Heke Rd, did not go into lockdown but kept its children indoors.
Among the parents who went to the school were a number originally from the United States for whom the words ''school lockdown'' had a more sinister connotation.
One father said his son called at 11.40am saying he had seen kids fighting, one of whom had a knife.
He and his wife rushed to the school but were asked to leave so they were waiting outside the school boundary.
The man, who did not want to be named, said his biggest concern was the initial ''information blockade''.
''We were told it was an ongoing situation, and that we'd be informed later.''
Another father said he had come to the school because it was better than waiting nervously at work.
He had also spoken to his son before students were told to turn their phones off so they wouldn't make any sound.
''My son sounded nervous but okay. He did manage to spit out there was a kid with a knife, so I figured it was probably just that. But I'm from the US so lockdowns at school make me nervous.''