A 14-year-old schoolgirl who held a knife to the throat of a younger girl while demanding her lunch has heightened concern over the level of violence some Gisborne schools are having to deal with.

The incident came just days after a fight was filmed at another school and posted on a video website.

A small group of Gisborne Girls' High School students approached another group of 13- to 14-year-old girls on the school field during lunch break last Wednesday.

Police said an altercation took place and a knife was used in a threatening manner.

The Gisborne Herald said it had been told a 13-year-old student was asked for her lunch, she refused, and her hair was grabbed and a knife held to her throat.

Details of the altercation remain unclear and investigations are continuing.

A parent of one of the girls approached said her daughter was shaken but "coping" and had returned to school.

"All of the parents, on both sides of the fence, are extremely upset at what has happened," she said. "A knife at a high school is something you don't want to see."

She did not hold the school responsible.

"Something like this is out of their control. It's not something you expect in a Gisborne high school," she said.

The school's board of trustees held a suspension meeting on Monday night to deal with three students.

Board chairman Ian Petty said one of the girls had since been excluded from the school, while the two others were on extended suspension pending further investigation by the school's senior management team and police.

Exclusion applies to students under 16 years old and means the school needs to help them find another form of education.

Girls' High principal Heather Gorrie said the situation affected a lot of people and it was important to allow due process to take its course effectively.

The school was understood to be supporting the victims.

The incident followed a fight at Gisborne Boys' High School that was filmed and posted on a video internet site the previous week.

Principal Greg Mackle said a group of boys "wanting to set up a fight club" brought boxing gloves to school and began fighting during an interval period. It is understood camera-phones were used to film the footage.

The incident was stopped by school staff "straight away".