Story highlights About 15,000 people attended "Deltopia" party near Santa Barbara, California

Party turned ugly when a police officer was hit in the head with a backpack

Five more officers -- Santa Barbara County deputies -- were injured

Stop signs were torn down, small fires ignited and police cars damaged

A street party turned into a violent melee that injured six police officers in a California beach community Saturday night.

About 15,000 people -- many of them students from nearby University of California, Santa Barbara -- crowded the streets of Isla Vista for the annual "Deltopia" celebration when "a major disturbance broke out," according to a news release from the Santa Barbara County Sheriff's Office.

It turned ugly when a UCSB police officer was "hit in the head with a backpack that contained large bottles of alcohol," causing a "significant head injury," the release said. A large crowd threw rocks, bricks and bottles at police officers who were arresting the person suspected of hitting the officer, it said.

A "major disturbance, emergency situation" was declared, and law enforcement officers from nearby Ventura County responded to help the Santa Barbara County deputies already on the scene, the release said. "Chemical agents and less lethal foam projectiles were deployed to disperse the crowds."

Five more officers -- Santa Barbara County deputies -- were injured, including one who was hit in the face with a brick, and two hit in the hand with bottles, the sheriff said. In all, more than two dozen people were treated at hospitals for injuries.

Stop signs were torn down, small fires ignited and property damaged, including several police vehicles, before order was restored early Sunday, the sheriff's office said.

At least 18 people were arrested in connection with the disturbance, while another 80 or so were arrested at other times during the party, the sheriff's office said.