A recorded message could be heard over the PA system saying the school was in lockdown.
Initially just one police car was outside the school but three more arrived before noon.
Officers could be seen searching the grounds.
Around 12.05pm the lockdown was lifted and students were evacuated to the sports field between the school and Kerikeri Domain for a roll call.
Parents were initially asked not to come onto the school grounds, but were later advised by email they could collect their children from 12.30pm if they wished.
An 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, whanau 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 on to the main field for a roll call.
''We have followed the instructions of the New Zealand Police throughout this event, and have kept all students safe and secure in their classrooms,'' Deputy Principal Mike Clent said in the email.
Kerikeri Primary School, which is directly across Hone Heke Rd from the high school, did not go into lockdown but did keep the children indoors.
