Police said multiple people had been shot but did not confirm the number or their status.
The victims were all found at a Fedex facility near the worldwide airport where the shooting took place late Thursday, police spokeswoman Genae Cook told a news conference, adding several others had been taken to hospital. The suspect shot himself and is among the nine dead, according to police.
Miller said he saw a man with what he described as "a submachine gun of some sort, an automatic rifle". "I immediately ducked down and got scared and my friend's mother, she came in and told us to get inside the vehicle". They encountered an "active shooter incident", she said.
She added that the gunman had died and the public is not believed to be in immediate danger.
The company said it is cooperating with authorities and working to get more information.
The latest rampage unfolded at a FedEx operations centre near the Indianapolis International Airport, after 11 p.m. local time on Thursday night. Safety is our top priority, and our thoughts are with all those who are affected, " the statement said.
The facility for the delivery company is reported to employ more than 4,000 people.
Two employees inside the building at the time told CNN affiliate WISH-TV that they heard as many as ten gunshots.
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The hospital did not immediately respond to a request for comment on his remarks. "He died after six or seven hours", he said. Outside a major city mortuary, weeping relatives gathered in the hot sun, waiting for the bodies of loved ones to be released.
Boillat told the television station that he "didn't exactly see a person get shot but, after hearing the shooting, I did see a body on the floor behind a vehicle".
"Luckily, I was far enough away to where he [the shooter] didn't see me".
Live video from news outlets at the scene showed crime-scene tape in the parking lot outside the facility. Less than a week later, 10 people were killed when a gunman opened fire at a grocery store in Boulder, Colo. Five people, including a pregnant woman, were shot and killed in January, and a man was accused of killing three adults and a child before abducting his daughter during an argument at a home in March.
Tens of thousands of people in the USA die each year due to gun violence.
The issue of gun regulation in the United States is politically fraught.
Earlier in April, weeks after taking office, President Joe Biden announced limited measures to tackle gun violence that included a crackdown on self-assembled "ghost guns".
"It's an global embarrassment", Biden told Congress members and gun control activists at a White House ceremony.
Republicans immediately attacked Biden's move.