EUREKA, Mo. (AP) _ A wagon hauling participants in a hayride overturned Friday night, killing one passenger and injuring up to 12 others.

Authorities were calling it a ``mass-casualty incident,'' meaning they feared there could be more injuries than emergency crews could handle. The Jefferson County Sheriff's Department confirmed the one fatality.

Between 10 and 12 people were injured. Three were in critical condition and one was in serious condition.

Authorities weren't sure what caused the wagon to overturn.

The accident happened around 8:30 p.m. at the Rocking J. Ranch in High Ridge just southwest of St. Louis.