A fight that broke out at a troubled South Los Angeles school escalated into a campuswide brawl involving as many as 600 students before it was quelled by police in riot gear.

The melee, which students said started around noon Friday between rival black and Hispanic gangs, forced authorities to shut down Locke High School and keep students in their classrooms. After restoring order, they rounded up students who hadn't returned to class and separated them by race, holding Hispanics in the gym and black students in another room.

Four people were arrested, three students for fighting and one non-student on suspicion of possessing a knife, Los Angeles school district spokeswoman Susan Cox said.

Several students were injured and treated at the scene, but nobody was hospitalized, officials said.

Music teacher Reggie Smith described to the Los Angeles Times a chaotic scene where it was difficult to distinguish between trouble makers and those trying to avoid the mayhem.

"The kids were crazy, running from place to place jumping on other kids," Smith said. "Some of my kids were crying because they were walking to class with friends and they got jumped."

Victor Wong, an 18-year-old senior, told the Times the melee grew out of a fight two days earlier between two graffiti gangs. He said Hispanic students who are friends of his asked him to participate in a fight planned for Friday that was to pit 10 Hispanic students against 10 black students.

The two groups met as planned at the handball courts, but the fight quickly spread throughout the campus, Wong said.

"Security didn't know where to go," he said. "They'd concentrate in one spot and something would happen somewhere else."

School district police brought in about 60 officers to the scene, while the Los Angeles Police Department dispatched about 50 officers and more than a dozen patrol cars.

Ronald White, a 17-year-old senior, said that when police arrived some of the students began fighting the officers, who responded with their batons. Another student said he saw police use pepper spray.

Locke has been marred by almost daily fights during much of the academic year, but students and teachers said Friday's brawl was the worst in years.

Joseph Sherlock, a senior, called it "my first actual encounter with a riot."

About 65 percent of the 2,600 students enrolled at Locke are Hispanic, and 35 percent are black.