The incident happened Friday evening at the Calaveras County Fair and Jumping Frog Jubilee in Angels Camp, Calif., about 50 miles east of Stockton, Calif. An official from the California Department of Forestry and Fire Protection told the San Francisco Chronicle the Yo-Yo ride collapsed and firefighters were alerted by screaming.

The three most seriously injured ride patrons were airlifted to nearby hospitals. Fifteen others with less serious injuries were taken by ambulance or drove private cars to hospitals.

Investigators from the California Occupational Safety and Health Administration were expected at the accident scene Saturday.