Bauwens, the Red Cross nurse, said many of the injuries happened when a brick fireplace in one shelter was ripped apart by the storm. The shelter was one of four where scouts had run for cover.

The National Weather Service was referring to the event as a tornado by late Wednesday. It said it received a report of a touchdown at 6:35 p.m.

Officials at Burgess Memorial Hospital, about 20 miles from the ranch, said they had treated several patients injured by the storm Wednesday night and that injuries ranged from minor to serious.

A spokesman for Mercy Medical Center in Sioux City said two children had arrived at the hospital by helicopter.

"These are traumatic injuries," said spokesman Mike Krysl, who said the regional trauma center is "in disaster mode."

Heavy downpours hit the region over the weekend, with more thunderstorms predicted for Wednesday night and Thursday morning.