Up to 100 students used knives, chairs and pieces of wood in a brawl that spilled from an Auckland street into a KFC restaurant.
Terrified staff locked themselves inside businesses on Massey Rd, Mangere, while others watched in horror as students received injuries bad enough to draw blood.
Five people were arrested by police, who had to send 13 units to subdue the crowds shortly after 5pm today.
Three youths and two adults had been arrested, police said.
A Mangere East KFC employee, who did not wish to be named, said about 30 school students burst into the restaurant.
"It was a really big fight between school students. They came down to our store and started punching a guy.
They just started smashing him.
"They just came in. They picked up chairs and everything."
She said the students were boys and girls, and looked to be under 16. Some appeared to be injured, and were bleeding and covering their faces with their hands, she said.
A large police presence quickly swamped the area, she said.
She saw students taken away in police cars.
"The police are taking statements from all of the people around here."
A local employee said the brawl could be the result of a school rivalry. She said the fight was "bloody terrible".
"It must have been two different schools But I don't know which schools because I wasn't going to hang around. I'm only a little person.
"I assume it's a school rivalry.
"It's terrible. It's disgusting. It's freaky. There are a lot of old people walking around here. They could get really frightened ... I'm frightened. I think I'll go the other way home tonight.
"I feel for those workers in there. I wouldn't be surprised if the bloody windows have been smashed."
A police spokesman said four people, two adults and two juveniles, were arrested following the incident.
"There were about 100 people there. Weapons used included knives, chairs and bits of wood."
He said CCTV would be reviewed and a "number of" schools would be visited tomorrow.
It was not clear what the fight was over, he said.
Staff at Mangere East Library said they saw about 100 people gathered outside the KFC before the fighting broke out.
"There was a swarm of at least 50, it could've been 100 of them, and they were running up and down the road and then it all started."
The staff members, who wished to remain anonymous, said they could see weapons.
They immediately locked the doors of the library once they saw the commotion in order to protect visitors.
"It looked like someone had a piece of ply[wood]. It was crazy. About 10 police cars turned up.
"They arrested about 15 people. Some of them didn't look like they were even school kids."
A school principal contacted by the Herald said he had not been contacted about the fight at 6.45pm.
"We will be onto it first thing in the morning and will take it seriously," he said. "We have a good relationship with other principals ... so will be in contact with them and the police."
An investigation and appropriate disciplinary action would be taken if required, he said.
A spokesman for another school said he had been informed about the fight.
"I can't comment at this stage because we are still unaware of the facts," he said. "What we are doing is we are going to meet ... tomorrow and ... get to the bottom of it."
Last year, footage went viral on social media of girls from a South Auckland school stomping and punching each other as police tried to break up the fight.
A Facebook page was set up earlier in 2015 which showed videos of fights between students at Auckland high schools, and police contacted the social networking giant in a bid to have the page taken down.
In May 2015 a 15-year-old girl was arrested after an assault in the Far North that was filmed and posted online.
And in July of the same year, a fight involving about 60 students from two Auckland schools broke out at Orakei train station over a photo posted to Facebook insulting an opposing school's rugby jersey.