A teenager was taken to hospital after being repeatedly punched in the head during a schoolyard fight which was videoed and sent to his classmates this week.

It is not clear how the fight started, but the Weekend Herald understands a 17-year-old boy was attacked by a friend at Lynfield College on Wednesday afternoon.

St John ambulance staff were called to the school to deal with the injured boy, who was then taken to Auckland City Hospital's emergency department.

The fight was captured on another student's cellphone and the video quickly sent to others in the school.

A parent discovered the video later that day and sent an email to the school's board of trustees raising concerns about the "disturbing and unspeakable behaviour".

The letter said the executive and board needed to deal with the matter promptly and ensure any wrongdoing was punished speedily.

It was also sent to a large group of parents "so they are informed of the unacceptable behaviour taking place in the school that their child attends, and could in turn be subject to".

Lynfield principal Steve Bovaird said the injured student was punched about four or five times and was accompanied to hospital by one of his deans.

He said the college had dealt with the matter. He was disappointed the letter writer had not gone to him with their concerns first.

Mr Bovaird said students with a copy of the video had been called into the dean's office and asked to delete it.

He has also sent a letter reminding parents that the school took violence seriously and had suspended the student, who will go before the board next week.

"This school has a very low tolerance for this sort of behaviour and if students want to engage init then they can know what to expect."

Mr Bovaird said it was difficult to prevent students filming fights as mobile phones were such a big part of life.

"It is a real issue for schools but it happens ... We have all had to learn with the digital age over the last 10 years."

Netsafe executive director Martin Cocker said the use of technology in bullying was increasingly common and could multiply the victim's pain many times over.

"There's a lot of debate about which form of bullying is worse - technology-based bullying because of its psychological damage, or physical bullying because of the damage that it brings.

"But in these cases you've got a combination of them both."

Mr Cocker said that while it was incredibly difficult to stop such bullying occurring, there would always be "voices of reason" in any community of young people.

"Those people should discourage the posting of this kind of material."