A fierce thunderstorm swept through a rural Wisconsin county that was packed with holiday campers. It toppled trees, killing an 11-year-old girl, blew boats ashore and injured more than three dozen people, officials said Saturday.

The storm moved across Minnesota and Wisconsin on Friday, packing winds approaching 80 mph and hail as large as softballs.

In northwestern Wisconsin's Burnett County, at least 39 people went to hospitals after the storm toppled hundreds of trees and left thousands of utility customers without power. Authorities said most of the injured were treated and released, but three were in critical condition.

A search was underway Saturday along the St. Croix River for missing canoeists, the Wisconsin Emergency Management Office said. Boats were blown ashore in the area, and an airport hangar in neighboring Douglas County collapsed.

Law enforcement officials reported the girl who died was killed when a tree fell on her at a campground in the county. No other details were immediately released.

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