An explosion at an Illinois ammunition factory killed one employee, authorities said.

"We were driving through there and heard a big boom, pushed the van a little bit," said Dustin Courtouise, who lives in East Alton, the site of Winchester ammunition.

The factory, which is owned by Olin Corp., is about 20 miles north of St. Louis on the Illinois side of the Mississippi River.

"There was a loud explosion heard throughout the town," East Alton Mayor Darren Carlton said.

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TV stations reported that the explosion Thursday involved a truck. Winchester said it would fully investigate the "tragedy."

"Our thoughts and prayers are with our employee’s family and coworkers," the company said in a statement.

Winchester’s manufacturing operations are located in East Alton and Oxford, Mississippi. It makes ammunition for various markets, including the U.S. military.