At least six people are dead in Montana after a wind storm caused 21 vehicles to crash together on the highway Friday evening, authorities said.
Among the dead were two children, The Associated Press reported.
The storms' heavy winds and zero visibility are believed to have contributed to the crash, officials said.
Montana Gov. Greg Gianforte confirmed the "mass casualty crash" on Twitter, where he encouraged his followers to pray for the victims.
"I’m deeply saddened by the news of a mass casualty crash near Hardin. Please join me in prayer to lift up the victims and their loved ones. We’re grateful to our first responders for their service," Gianforte tweeted.
It was not immediately clear how many people were injured in the crash.
Montana Highway Patrol Sgt. Jay Nelson said emergency crews responded to the major crash on Interstate 90, which they believed was caused by dust storms and a thunderstorm.
"It appears as though there was heavy winds, causing a dust storm with zero visibility," Nelson said.
Nick Vertz, a National Weather Service meteorologist in Billings, said dust storms initially popped up in central southern Montana around 1 to 2 p.m. These dust storms then made way for a severe thunderstorm that remained until 9 p.m. Friday.
The crash happened around 4:30 p.m., likely by an "outflow" — a gust of wind that can travel faster than the storm that produces it — that flew ahead of the storms, Vertz said.
Videos taken at the scene showed the wrecked vehicles caused a miles-long backup.
First responders remained on the scene through the night to clear the wreckage.
The Associated Press contributed to this report.