The incident occurred at a FedEx facility on Mirabel Road, Indianapolis, late on Thursday night.
At least four people were hospitalised, including one person with critical injuries. Two others were treated at the scene and released. The facility is located close to the Indianapolis International airport.
In an earlier tweet, Perrine said Interstate 70 near the facility was closed in both directions, but it was later reopened.
There has been a spate of mass shootings across the United States in recent weeks.
It's unclear how many workers were on duty during the shooting. Less than a week later, 10 people were killed when a gunman opened fire at a grocery store in Boulder, Colo.
US President Joe Biden recently announced six new measures he said would help curb gun violence, a phenomenon he described as "an worldwide embarrassment".
A witness says he "saw a man with a submachine gun of some sort, an automatic rifle, and he was firing in the open". The company said it is cooperating with authorities and working to get more information.
A reporter with WRTV, an Indianapolis station, posted an interview on Twitter with a man who said he had been at the facility when the shooting broke out and later saw a body on the floor.
"Safety is our top priority, and our thoughts are with all those who are affected".
Family members gathered at a nearby hotel to await word on loved ones.
Local media cited a company spokesman as saying that FedEx is now considering reevaluating a policy that prohibits employees from having their phones with them during shifts, making it hard to contact them.
Footage from the scene shows police tape in the auto park outside and multiple emergency service vehicles.
Another man, Ian Johnston, told the news outlet that his wife, who works at the facility, had texted to tell him there was an active shooter inside.
Eight people shot and killed at a FedEx facility in the United States city of Indianapolis.
Another witness said his niece was sitting in her auto when the gunfire began. As officers arrived, they came upon an active shooter, she said. "She's fine, she's in the hospital now".