Wellsville ? A boy was killed and nearly three dozen people were injured Saturday in a northeast Kansas pile-up that left wreckage from dozens of vehicles strewn across Interstate 35.

Thick fog enveloped the highway when the first accident happened around 7 a.m. between Wellsville and Ottawa in Franklin County.

Jane Konzem of the Kansas Highway Patrol told The Associated Press that a tow truck operator was assisting a disabled vehicle when the truck was hit. That crash triggered a series of accidents involving about 30 vehicles.

Konzem said the victim died in the largest of the crashes, which involved six tractor-trailers and 13 other vehicles.

Franklin County Sheriff Craig Davis didn’t immediately return calls from the AP but told The Ottawa Herald that the victim was a 3-year-old boy who had been traveling with 10 other people to Mexico. The boy reportedly was not wearing a restraint.

Konzem didn’t know how many people were injured. But an area newspaper reported 10 people were hospitalized — six critically injured and four with serious injuries. About two dozen others were treated for minor injuries.

Konzem said the pileup closed the interstate for hours, and authorities sorted through the wreckage into the evening. “I know a couple of tractor-trailers jackknifed,” Roger Lippert, division chief of Johnson County Med-Act, said.