More than 20 people were riding the carnival raid, called the Yo-Yo, when it collapsed shortly after 6 p.m. Friday at the Calaveras County Fair and Jumping Frog Jubilee in Angels Camp in the Gold Country, authorities said.

24 people were injured, including three seriously. The three seriously inured were airlifted, one each to UC Davis Medical Center in Sacramento, Doctors Medical Center in Modesto and Memorial Medical Center in Modesto, said Lisa Williams, a spokeswoman for the California Department of Forestry and Fire Protection.

Fifteen persons, who were less injured, were taken by ambulance to three other area hospitals.

The ride has metal arms that, each with a seat at the end attached by a chain, that fling out as they spin around a center pole, putting the seats horizontal to the ground. The pole apparently collapsed, causing the arms to crash back toward the center, said Dennis Townsend, a chief in the Calaveras County unit of the California Department of Forestry and Fire Prevention. A team of firefighters arrived at the scene of the accident and they called for help.

State accident investigators were on their way to the fairgrounds and would conduct the primary investigation into the accident, Williams said.

The Calaveras County Fair and Jumping Frog Jubilee, inspired by a Mark Twain story, titled “The Celebrated Jumping Frog of Calaveras County,” focusing on a character and his jumping frog, opened Wednesday; it is held each year in May.