The stabbing of a student outside De La Salle College in Māngere on Friday afternoon involved students from another school, police say.

A 16-year-old boy was taken to hospital with stab wounds after a group of about 30 male youths attacked school students outside the gates of the college on Gray Ave at 4.20pm.

"The incident was reported to have involved students from two separate schools," a police spokeswoman said.

She did not say which school the other group of students came from.

The spokeswoman said police were continuing to make inquiries to determine what had occurred.

De La Salle College principal Myles Hogarty has been contacted by the Herald for comment, but has not returned calls.

Hogarty had earlier sent an email breaking the news to parents, announcing two students had been hospitalised after the attack.

"Our students had just finished rugby training and after-school tuition classes and were heading to the Middlemore train station to catch trains home," Hogarty wrote.

"A group of around 20-30 male youths attacked De La Salle students outside our College Gates."

Hogarty said two students were taken to Middlemore Hospital one for a concussion and another for an "abdominal injury".

"Their injuries while concerning are not life-threatening and one student will be discharged later this evening [Friday]. College staff accompanied the two students and stayed with them until their parents arrived."

Hogarty also touched on the drastic response the school took during the attack.

"All of our young men were herded back into the College and supervised by staff before being allowed to leave only with their parents," he said.

"Details as to who these youths were are still sketchy and the police are looking at CCTV footage from the train station to identify them."

A witness told the Herald students from the school appeared to have been attacked by a group of older boys or adults outside the school gates.

The witness said the injured boy was in a group which was walking towards the commotion when they were attacked by "grown men".

In the ensuing scuffle, the boy was stabbed in the stomach.

"He was in a pool of blood," the witness said. "And the teachers had to drag him back in the gates - it was that bad."

Another boy was believed to have been knocked out in the brawl.

It was not known what started the fight. But the witness said it appeared to be organised and there were reports that a few people had weapons.

"It was unprovoked. When the fight broke out, every single student that was walking was getting attacked. The school was rushed.

"The boy just walked out of a shop. They could see all the commotion happening, but they were right away from it. Then they were boxed in."

Police responded to reports of disorder on Gray Ave at about 4.25pm.

St John Ambulance said one person was transported to Middlemore Hospital with moderate injuries.