Owner of Wickman Way Pricecutter, Jagjit Janjua, said from his grocery store opposite the school gate that he could see crowds of kids leave the school and rush to a nearby carpark.
He said it looked like the whole school was following the fight. He knew something was wrong when a teacher asked him to call police.
"We saw them all go up the road and my wife called police and ambulance."
The dairy is often packed with students after school, he said.
"They're good kids, well-behaved kids, and we treat them like our own kids."
It follows a stabbing at a South Auckland school earlier today. Police said the two incidents were not connected in any way.
A police spokesman said it appeared there were no other people involved, and they are talking to witnesses.
The investigation is in early stages, with a scene examination taking place, and police said it will take some time to fully establish details.
Police earlier said an altercation had taken place between two groups of youths.
