An employee got into an argument with a supervisor early on Wednesday, then shot and killed four people at a western Kentucky plastics plant before killing himself, police said.
The shooting happened at Atlantis Plastics in Henderson, an Ohio River town of about 28,000 people.
Police Lt David Piller said two others were injured and flown to hospitals in Evansville, Indiana. At least one was in critical condition, officials said.
The shooting victims were scattered around the plant, Piller said, and the employee had apparently retrieved the handgun used in the shootings during a break.
"It appears the shooting was random at this time," Piller said.
Police did not say if the supervisor the employee argued with was among the victims.
A woman who answered the phone at a number for Atlanta-based Atlantis Plastics declined to give her name and would only say that the company would not comment until a 3 pm news conference.
Names of those involved in the shooting have not been released.
Hours after the shooting, police had set up a roadblock on the street leading to the plant, which is in an industrial area on the southern side of Henderson.
Other employees at the plant were sent home.
In a news release on the company's web site, Atlantis Plastics said it is a leading US manufacturer of three kinds of products: polyethylene stretch films for wrapping pallets of materials, custom films for industrial and packaging uses, and moulded plastic pieces used in products such as appliances and recreational vehicles.
The company has 700 employees, including 200 in Henderson, according to business directory Hoovers.