Up to 35 people are reported to have been shot at a factory in Goshen, Indiana.
The incident happened at the Nu-Wood Decorative Millwork, a vinyl siding factory on an industrial estate.
The Elkhart County Sheriff's Office said it had been told the shots were fired by a white man who was still at large inside the building and who may have been a former employee of the company who is also a firearms dealer with access to several kinds of weapons.
"We're hearing as many as 35 have been shot but we can't confirm that," said a Goshen police dispatcher.
Hospitals confirmed that at least four people were being treated for injuries. Reports from the scene indicated the four were able to flee the factory after the shooting but other possible victims remained inside.
As many as 60 people may have been at work inside the building at the time of the mid-afternoon shooting.
Police surrounded the building and a team was poised to storm the building.
Local television aerial pictures of the scene showed ambulances lined up in a parking lot at the industrial park.
Goshen, about 100 miles west of Chicago, has a population of 30,000.