Whangaparāoa College students were told to stay in their classrooms today after police received a report of a threat involving a firearm.
A post on the school's Facebook page from earlier today said all students were safely in their classrooms with teachers after the school was locked down.
Students have now been released from classrooms.
People picking up students from school were advised to wait in their cars and to not come into the school until further notice.
The school has since posted on Facebook that police had advised it was safe to release all students and lift the lockdown.
"Thank you for your patience and understanding while we ensured everyone on site was kept safe from a potentially dangerous situation," the post said.
Whangaparāoa College principal Steve McCracken said the incident involved a past student.
The school was placed into lockdown at 2.45pm and the lockdown was lifted at 3.35pm.
Everything was back to normal now and school would resume tomorrow morning, he said.
Police said they received a report that a non-specific threat involving a firearm had been sent to some students at Whangaparāoa College.
The school was placed in lockdown as a precaution, police explained.
Enquiries identified the person involved in making the threat and police are speaking to those involved.
The firearm reportedly involved has been confirmed as an imitation firearm and will be destroyed, police said.
The young person involved will be referred to youth aid.