Updated 10:25 a.m. ET
HUNTINGTON BEACH, Calif. Police say crowds in the aftermath of the U.S. Open of Surfing refused to leave downtown Huntington Beach, and officers in riot gear had to clear the streets as fights broke out and property was damaged.
They referred to the trouble as a "major event," reports CBS Los Angeles station KCBS-TV.
Police say when the Open's eighth and final day ended Sunday, officers were unable to get an increasingly rowdy crowd to disperse from surrounding streets.
Local police declared an unlawful assembly, summoned all its officers to duty and brought in help from other cities.
Police say city vehicles, portable toilets, newspaper racks, broken windows and street signs were damaged.
An eyewitness reported seeing several windows being smashed and at least one store -- a skateboard and bicycle shop -- being looted by vandals, KCBS says.
At least 8 arrests were made for failure to disperse as streets were cleared and order restored after about two hours, police said. Arrests were made for disturbing the peace, unlawful assembly and inciting a riot. One person was held for assault with a deadly weapon on an officer. Police will look at video, and more arrests could be made.
There were no immediate reports of injuries.
A video on YouTube purported to show police tossing a tear gas canister. Another video showed about a dozen men kicking over Porta Potties -- it's alleged that was the flashpoint of the disturbance, the station says.
The weekend surfing competition drew thousands of people to Huntington Beach, a popular surfing spot.