A gun was pulled out during a fight between Ōtāhuhu students earlier this week and held to a young woman's head.
Two girls in school uniform can be seen fighting, grabbing each other by the hair. As the pair continue to fight a group surrounding them can be heard yelling.
"Motherf***er" one person yells.
Later in the footage, a woman is seen holding what appears to be a gun.
She holds the gun up, pointing it at a person in a green jumper while screaming at her.
"You touch my sister again, touch her, touch her," the woman with the gun yells.
She then walks over to the woman in the green jumper and presses the gun to her head.
"Get the f*** out of here right now," the woman yells while still holding the gun.
The Herald understands the fight took place on Thursday afternoon.
Principal Neil Watson confirmed the school had been made aware of the video on Saturday and police are now investigating.
He did not know if the gun shown in the video was real.
A police spokeswoman said they received a report of a disorder incident in Otahuhu on Thursday afternoon just after 4pm.
"It was a report of a group of people fighting. Inquiries are underway to speak to those involved to establish the circumstances."
The Herald was sent the video by a parent from the school, who was concerned about her children's safety after seeing the incident.
"I am keeping my child at home until I hear back from the school that this has been resolved and some sort of consequences is there with these students."
Asked if the school had sent out any messaging to parents, Watson said the school was not at that stage yet.
"We have a member of the public with what looks like a firearm. We're helping the police with their inquiries, and our priority is the safety and security of our families and students."
The 19-year-old disappeared without her wallet or mobile phone.