Two children from Ontario were among those killed Thursday in a massive vehicle pileup on a Detroit highway near the Canadian border.

Michigan State police said the children, aged seven and nine, were from Windsor, Ont. and they were related. They have not yet been identified.

An adult travelling in another vehicle was also killed. According to the WDIV Detroit TV station, he was a 54-year-old man from Allen Park, Mich.

At least 20 others were injured, two of them critically.

Six separate crashes involving at least 30 vehicles occurred over a two-kilometre stretch of Interstate 75 as snow squalls reduced visibility in the area. The highway was also slippery, preventing many vehicles from stopping in time to avoid the pileup.

Video footage showed jackknifed tractor-trailers and heavily damaged cars scattered across the highway. A number of people were able to walk away from their vehicles unharmed.

“We’ve had accidents…in this state that have gone up to 100 cars before, but this is one of the worst ones I’ve seen in the Detroit area,” said Lt. Michael Shaw.

A fuel truck driver told The Associated Press the whiteout conditions came suddenly.

"I looked on my driver's side mirror, and I could see the trucks piling up back there," Greg Galuszka said.

"Then, when I looked in my passenger side (mirror), is when I saw the steel hauler coming up. I just said my prayers from there and said, 'Please don't hit me."'

Phillip Bost, who was driving a semi-truck, said he rushed to help the injured.

"I heard booms and bangs behind me. Boom, boom, boom, boom," he told AP.

There were "people bleeding, people limping, people shaken up. It was a bad ordeal," he said.

With a report from CTV Windsor