AMES, Iowa -- Damage is "extensive" after a yearly festival near Iowa State University turned ugly early Sunday morning, police said.

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Video: Raw Riot Footage Slideshow: VEISHEA Riots

Police said officers used tear gas on a crowd of about a 1,000 after the mob attacked cars, broke store windows and uprooted streetlights in Ames.

About two dozen people were arrested on charges ranging from disorderly conduct to assaulting a police officer.

Officers said they took a call around midnight Sunday night that a group of several hundred people was getting out of hand. People in the crowd reportedly tossed bottles and cans at police, yelling, "riot, riot!"

It took more than five hours for police to break it up.

About 20 people were treated at the hospital, mostly for skin and eye irritations from the tear gas.

The annual campus fair has experienced trouble before. The university banned alcohol sales after a man was killed following the festival in 1997.

The Ames Police Department, the Iowa State Department of Public Safety, the Story County Sheriff's Office and the Iowa State Patrol were called in to bring the situation under control.

The event, called VEISHEA, was named in 1922 for the five colleges at Iowa State: V standing for Veterinary Medicine, E for Engineering, IS for Industrial Science, HE for Home Economics, and A for Agriculture.

The event's Web site touts VEISHEA as "the largest student-run, alcohol-free celebration of entertainment and education in the nation and second-largest in the world."

College officials said they will now meet to determine the future of VEISHEA and whether it will return next year.