Eight other people were taken to hospital.
County Sheriff Billy Sollie confirmed the deaths and injuries at the Lockheed Martin plant in Meridian, Mississippi.
“He had a shotgun and a semi-automatic rifle and he appeared to open fire at random on employees,” he said.
Sollie said no other individuals were involved and his officers were securing the scene. Investigators did not know of the motive, he said.
Sollie didn’t release the name of the gunman but said he was a Lockheed Martin employee. He had no information on whether the man had been in trouble with his employers.
Officials at the plant declined to comment and a Lockheed Martin national spokeswoman was unavailable to immediately provide details.
“We’re just trying to gather information and are working with state and local authorities to determine the details of the incident,” said spokeswoman Meaghan Mariman from the company’s headquarters in Maryland.