The pukeko was killed by a Botany Downs Secondary College student.

The SPCA is investigating a video of a teenager ripping apart a pukeko in what has been described as a "cruel" and "sadistic" act.

The video was posted online and has been widely shared among students from Botany Downs Secondary College.

In the clip a teenage boy is shown pulling the pukeko's body in half from its wings.

Auckland SPCA chief executive Andrea Midgen said the video appeared to show "cruelty to the nth degree" and the organisation was pursuing possible charges of animal cruelty.

Depending on how the bird was killed, that could also constitute an animal cruelty charge "if they hadn't killed it in a humane way," Midgen said.

Inspectors were alerted to the video on Friday night and would be investigating over the weekend.

It was unclear whether the bird was dead when it was torn apart.

The video circulated online on Friday and many Botany Downs students were left "traumatised", one classmate said.

"Everyone was disgusted and appalled, it was really, really bad," the student, who asked not to be named, said.

"We just felt like we don't ever imagine seeing that kind of behaviour, it's sadistic.

"It's pretty much torture."

The student said it was believed the boy featured in the video had killed the pukeko with a stone.

He said the native bird may have still been alive when it was ripped in half.

"Everyone's been saying it wasn't dead. And the guy sarcastically claimed he was hungry."

He said some students at the school had threatened the boy.

Botany Downs Secondary College principal Karen Brinsden told NZME staff were aware of the video and had spoken to the student.

Brinsden said the student told the school he killed the bird in a shooting expedition.

He said the video showed him "breasting" the bird in preparation for cooking, NZME reported.

Brinsden said since the incident took place on a rural property outside school hours there was no reason to take any course of discipline.

"As a school we do not condone cruelty to any wildlife or animal."