(CNN) -- A trailer came unhitched from a truck near Syracuse, New York, on Wednesday, and slammed into an approaching minivan, killing seven people, authorities said.
Four of the dead were children from two families, police said.
The one survivor from the van is Shawn Mead, whose children Alyssa, 7 and Tyler, 4, died in the crash. He's in a hospital, and the extent of his injuries are not yet known, police said.
Teresa Bush, 26 and her two daughters Jasmine, 5, and Alexis, 4, died in the crash, along with Lena Beckwith, 21, and Carino Vanorden, 24. It was not immediately clear how the adults may have been related.
The two people on board the truck -- Ryan Dorward, 26, and Duane Newton, 44 -- were unharmed.
Authorities do not know what caused the trailer to come loose. Storms and hail were reported in the area Wednesday evening, but Sheriff's Lt. Robert Derksen told CNN affiliate YNN Syracuse that weather was not believed to be a factor.
The station also reported that the trailer was carrying about 20 crushed cars to a dump.
The crash took place on a rural highway in the town of Truxton, said Capt. Mark Helms of the Cortland County Sheriff's Department.
Autopsies are being conducted Thursday and Friday, coroner Whitney Meeker said.
CNN's Jake Carpenter contributed to this report.