CAMPBELL COUNTY, Wyo. — A tornado that ripped through the country’s largest coal mining site in northeast Wyoming left eight people injured and halted operations as first responders searched the massive open-pit site for employees and continued to assess the damage, officials said Saturday.

The tornado hit the North Antelope Rochelle Mine in Campbell County around 6 p.m. Friday during a shift change, initially complicating search and rescue efforts. But Peabody Energy, the operator of the mine with headquarters in St. Louis and South Brisbane, Australia, confirmed before midnight that all employees had been accounted for.

Six employees were still being treated in hospitals as of 11 p.m. Friday, the company said. No deaths were reported.

Melissa Smith, a meteorologist, and hydrologist with the National Weather Service in Rapid City, South Dakota, said a storm system scattered tornadoes throughout Campbell, Natrona, and Johnson counties.

“The tornadoes would form, come down, stay on the ground, and come back up,” Smith said.

At the mining site, empty train cars and buses there to transport workers were blown over, according to Leslie Perkins, spokesperson for Campbell County. First responders also had to contain “various hazardous materials” that leaked after the tornado touched down, the Campbell County Fire Department said in a statement, although the agency did not provide more details about the leaks.

Each year, Wyoming sees an average of 10 to 12 tornadoes that “tend to be quick spin-ups that are not that big,” unlike Friday night’s twister at the mining site, said Aaron Dye, another National Weather Service meteorologist.

“Seeing that size of a tornado is pretty different,” he said, adding that meteorologists were on the ground Saturday morning in Campbell County taking measurements. Dye said the weather agency will release more information later Saturday.

Meanwhile, operations at the mining operation about 64 miles south of Gillette will remain suspended until damage assessments at the facility are completed, Peabody said in a statement.

The mining site is the largest in the country, according to the U.S. Energy Information Administration. It produced nearly the same amount of coal in 2021 as Illinois and Montana combined, the fourth and fifth largest coal-producing states.