Lt. Michael Shaw says the children, a 7-year-old boy and 9-year-old girl from Windsor, died in the almost two-kilometre-long series of crashes. An adult in a different car was also killed and at least 20 others were injured.
Shaw said visibility was extremely poor when the mass of crashes happened on Interstate 75 on the southwest side of the city. The injured, also including children, have been taken to hospitals.
A similar pileup west of Indianapolis involving more than 40 vehicles closed Interstate 70 in both directions.
There was no immediate word on injuries, but the roadway was expected to be closed for several hours.
In Detroit, SUVs with smashed front ends and cars with doors hanging open sat scattered across the debris-littered highway, some crunched against jackknifed tractor-trailers and tankers. Rescue crews went vehicle to vehicle in the search for survivors and to provide aid.
Motorists and passengers who were able to climb out of their vehicles huddled together on the side of the road, some visibly distraught, others looking dazed. A man and woman hugged under the grey, cloud-filled skies, a pair of suitcases next to them and a bumper on the ground behind.
Conditions went from "clear to total whiteout in a matter of seconds," Shaw said. "All of a sudden, they couldn't see anymore."
More than 40 vehicles were involved in two other chain-reaction crashes in Michigan.
U.S. 23 in Grand Blanc Township near Flint was closed Thursday after more than 20 vehicles crashed during a sudden snow squall. In southwest Michigan, eight tractor-trailers and six cars crashed on I-94, closing the westbound lanes to traffic at Paw Paw in Van Buren County.
About 30 vehicles were involved in the pileups in Detroit and scores more were trapped on the freeway behind the accident scene for hours. Shaw expected the freeway to be fully reopened sometime in the afternoon.
Greg Galuszka was driving a fuel truck along I-75 when white-out conditions quickly materialized.
"I looked on my driver's side mirror, and I could see the trucks piling up back there," Galuszka said, pointing to a mass of twisted metal where vehicles had smashed into each other a short time earlier.
"Then, when I looked in my passenger side (mirror), is when I saw the steel hauler coming up," he said. "I just said my prayers from there and said, 'Please don't hit me.'"
Phillip Bost was driving a semi-truck loaded with auto parts when the snow squall hit. Bost said he rushed to help the injured when alerted by the terrific sound of the crashes.
"I heard booms and bangs behind me. Boom, boom, boom, boom," said Bost of Ypsilanti.
There were "people bleeding, people limping, people shaken up. It was a bad ordeal," he recalled several hours later. "I'm quite shaken up."
Shaw said many people had to be pulled from their vehicles. Numerous fire engines and ambulances were at the scene.
The crash happened as snow and strong blustery winds reduced visibility across southeastern Michigan, said Bryan Tilley, a meteorologist with the National Weather Service in Oakland County's White Lake Township.
"There was a pattern of snow showers moving through the area in the midmorning hours," Tilley said. Nearby Detroit Metropolitan Airport had west winds at 20 miles per hour, with gusts to 33 mph around the time of the crash. The temperature of 24 degrees was about 30 degrees colder than a day before.
The crash happened near an elevated stretch of expressway where the road surface can cool quickly and make driving hazardous, Tilley said.
Lisa Czarnecki said she hurried to the crash scene from her office in downtown Detroit after her husband, Ken, called to say he had been involved in the crashes. Ken was driving at about 30 miles per hour when the vehicles in front of him suddenly stopped but he wasn't able to stop too, leaving "the front of his car under that white semi," she said, pointing to the highway.
"After I identified the car to one of the (emergency) workers, I asked them to go tap on the window and ask him to wave out the door," Lisa Czarnecki said. "They managed to get him out of the vehicle and he stood up and waved."
(With files from CKLW)