Authorities said the man shot six people at Atlantis Plastics before turning the gun on himself, WFIE-TV, Evansville, Ind., reported. Five people, including the gunman, died at the scene. The sixth death occurred at an Evansville hospital.
The seventh victim remained hospitalized in Evansville and was responding to treatment, officials said.
Witnesses told WFIE-TV the alleged shooter argued with a supervisor and left the plant. When he returned, witnesses said he shot the supervisor and walked through the plant, shooting at other employees.
The shootings occurred in several areas of the building.
Police said first-shift workers were asked not to report to work, WHET-TV, Evansville, reported.