Several fights erupted during the lunch hour Friday at Moreno Valley High School and five students were detained, according to the Sheriff's Department.
The scuffles occurred around 12:30 p.m. in the quad area of the high school at 23300 Cottonwood Ave.
A Riverside County sheriff's school resource officer and security guards were unable to contain the melee, prompting the deputy to call for backup.
Fifteen sheriff's units responded, and peace was restored within minutes, with at least five suspected combatants detained.
"We're conducting an investigation, trying to do find out who was involved in what, and who instigated what," said Riverside County sheriff's Deputy Herlinda Valenzuela.
She said no one was seriously injured in the altercations, but paramedics were called after a teenage girl nearly collapsed from hyperventilating.
The teen did not require hospitalization, Valenzuela said.
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Students were ordered back to class, and the high school was briefly locked down.
Deputies remained in the area Friday afternoon, and responded to the school again around 3 p.m. when students were released for the weekend and began massing near the front of the school. There were no additional reports of violence, however.