ANGELS CAMP, Calif. -- A carnival ride collapsed Friday evening at the Calaveras County Fairgrounds in northern California, injuring 24 people.

A swing ride called the Yo-Yo collapsed just after 6 p.m., Cal Fire's Lisa Williams said, reported KCRA-TV in Sacramento.

According to witnesses, 25 people were on the ride at the time.

The Yo-Yo has arms that fling out as they spin around an axis, said Dennis Townsend, a chief in the Calaveras County unit of the California Department of Forestry and Fire Prevention.

State accident investigators were en route to the fairgrounds Friday night.

Laurie Giannini, the fairground's marketing director, said the fair remained open Friday night but the carnival area was shut down following the accident.

There were no fatalities, Giannini said, and the riders who received minor injuries had been treated.

Three patients in serious condition were airlifted to area hospitals, and the others were taken for medical treatment by ambulances and Calaveras Transit buses.

The Calaveras County Fair and Jumping Frog Jubilee is held each year in late May and was inspired by the Mark Twain story, "The Celebrated Jumping Frog of Calaveras County."

Twain's tale focuses on a character and his jumping frog, named Dan'l Webster. The fictional frog-jumping contest is rigged in one gambler's favor when he secretly fills his opponent's frog with buckshot.

The Calaveras County fairgrounds is located just outside the Gold Rush-era town of Angels Camp in the Sierra Nevada foothills, about 80 miles southeast of Sacramento. It bills itself as an "old-fashioned county fair" with exhibits and a variety of entertainment.

Last year's jumping frog contest drew 4,000 entries. This year's final is scheduled for Sunday.

The jubilee has been held since 1928, according to the Union Democrat newspaper of Sonora.