One person also was killed in Indiana when at least 20 vehicles piled up - also in heavy fog - on a highway east of South Bend. Numerous others were injured.
Fog can be caused by warm air moving over snow; in Michigan Wednesday, temperatures had risen to over 50 degrees and the National Weather Service had issued a dense fog advisory for the area, warning visibility could be less than a quarter mile.
The first fatality in the Michigan pileup was a 14-year-old boy who was killed when the sport utility vehicle he was riding in and about 10 other vehicles - including a tractor-trailer - crashed on a fog-shrouded section of Interstate 96 outside Lansing Wednesday afternoon. The boy's mother and grandmother are in critical condition.
Ingham County Sheriff Gene Wriggelsworth says the other fatal crash occurred about 30 minutes later when a man hit a semitrailer from behind.
The Lansing State Journal reports many drivers said the fog was so thick at times that they couldn't see the cars in front of them until it was too late.
Police, reports the Journal, believe the cause of the pileup was a combination of poor visibility and vehicles failing to slow down enough in reaction to the weather.
A total of 114 vehicles were involved in pileups in the eastbound lanes, while between 80 and 100 vehicles crashed in the westbound lanes, the sheriff's department said.
At least eighteen people were being treated Wednesday evening at a hospital in Lansing. State police closed a 12-mile stretch of the highway in both directions following the accidents. The eastbound lanes were reopened late Wednesday, but the westbound lanes remained closed.
David and Janet Morrow of South Bend, Ind., said their son, Christopher, called from his cell phone on I-96 and told them, "I'm standing here in the road and I'm not sure how I got here." He told his parents his car "folded up like an accordion" when it crashed.
The chain-reaction collision in Indiana left wrecked vehicles scattered Wednesday morning in both directions over a three-mile stretch of the Indiana Toll Road, state police Sgt. Rodger Popplewell said. Police closed a 43-mile stretch of the highway for more than six hours.
Popplewell said a man riding in a van was killed when the vehicle was caught between two tractor-trailers.
Two ambulances were also struck by semitrailers as paramedics treated injured drivers, Popplewell said. No emergency workers were hurt.
Popplewell said that even hours after the crashes, fog was still rolling in off the snow-covered fields along the highway as temperatures reached about 50 degrees.
"Visibility was down to 20-25 feet when I was approaching the scene," he said. "The fog would disappear and then reappear, so it caught motorists completely by surprise."
At least seven injured people were treated at hospitals in the Indiana crashes.
Elsewhere in Indiana, numerous roads were closed Wednesday because of flooding.
Gov. Mitch Daniels - touring flood-damaged areas Wednesday in Hazleton and Washington, in the southwestern part of the state - said he will push for quick approval of federal assistance to help residents recover.