EUREKA, Mo. (AP) _ A wagon carrying several members of a Girl Scout troop on a hayride overturned Friday night, killing one passenger and injuring at least 17 others, authorities said.

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 fatality.

The accident, which involved members of the St. Rafael Church in south St. Louis, happened around 8:30 p.m. at the Rocking J Ranch in High Ridge, about 10 miles north of Eureka.

Several ambulance crews helped transport victims to multiple hospitals. At least four people were critically injured.

Sheriff's Deputy James Winkleman said it wasn't clear what caused the wagon to overturn, except that the horses had been startled by something.