A Facebook threat posted by a Canterbury teenager that sparked an international police response has highlighted the serious effects of cyber bullying on young people, say experts.

The 16-year-old Rangiora High School student posted a comment on his Facebook page on Thursday saying he had been bullied and would "go to school and shoot everyone in sight".

A woman in North Carolina alerted United States authorities after her stepson saw the message.

Police in the US quickly responded to the threat, which said the boy lived in "Mt Heaven, Texas" - similar to the town of Mt Haven in the same state - and contacted the school principal.

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The New Zealand boy had since confessed that the comment was a joke in response to Facebook bullying he had suffered, said school principal Peggy Burrows. Although the incident had been embarrassing for the school it had also drawn attention to the "unprecedented" level of cyber bullying and its effects, she said.

"It hurts kids' feelings but on a deep level it completely destroys their world - there's no escape from it ... I think parents need to wake up to it."

This week she will tell students at assembly they are not invisible on the internet, and she will talk about the far-reaching effects of cyber bullying.

Psychologist David Stebbing said he saw an average of one student a fortnight about issues related to cyber or other forms of bullying. Often young people felt they could say things on the internet they would never say to someone's face.

Principals' Federation president Peter Simpson said the key to prevention was young people speaking out if someone was being bullied.