First responders and police officers shut down a freeway due to an accident involving multiple cars and semi-trucks in Detroit, Michigan January 31, 2013. Three people were killed and roughly two dozen injured in a series of crashes involving 30 to 40 vehicles in "white-out" conditions along a slippery stretch of highway in Detroit, state police said on Thursday. REUTERS/Rebecca Cook

Two children from Windsor, Ont., died in a pileup involving more than two dozen vehicles on a Detroit highway Thursday, police said.

A 7-year-old boy and 9-year-old girl were killed on Interstate 75 at about 9:15 a.m., police said.

The children's mother is in critical condition and the father is being treated for non-life-threatening injuries at a Detroit-area hospital, Lt. Michael Shaw of the Michigan State Police said.

One man from Allen Park, Mich., in a different vehicle, was also killed and 12 others were injured — two critically, police said.

Shaw said about 30 semis, cars, trucks and SUVs collided in the chain-reaction crash, which witnesses said was due to whiteout conditions.

"The visibility on the roadway went from good to nonexistent in a matter of seconds," Shaw said.

The highway was cleared Thursday afternoon and has reopened.