A former FedEx employee killed eight people at a FedEx facility in Indiana, Indianapolis, the company said.
The police identified the suspect as a 19-year-old Brandon Hole, who last worked at the company in 2020.
He began shooting “randomly” almost immediately after exiting his car, according to police.
Seven people were also injured and the gunman apparently killed himself before police arrived, officials say.
This is the latest incident in a recent increase in mass shootings across the US.
At least four of those killed were members of the Sikh community, according to local media. Gurinder Singh Khalsa, a leader of the local Sikh community said the FedEx facility was known for employing members of the community who did not speak fluent English.
A statement from FedEx chairman and CEO Frederick Smith described the incident as a “senseless act of violence”.
“First and foremost, I want to express my deepest sympathies to the families, friends, and co-workers of those team members. Our priority now is in responding to the situation on the ground and helping our team members and law enforcement,” the statement said.
Ordering flags to be flown at half-mast, President Joe Biden described the recent mass shootings as a “national embarrassment”.
“It has to end,” Mr Biden said. “Every day there’s a mass shooting in the United States if you count all those who were killed out in the streets of our cities and our rural areas, it’s a national embarrassment and it must come to an end.”
In a news conference on Friday, city officials said no motive had been established yet, and noted that one may never be determined.
“We’ll never really know all the ins and outs of why this occurred, but we’ll try our best,” said police chief Randal Taylor.
Four people were found dead outside the building, and another four inside.
The attacker, who appeared to have shot himself “minutes” before police arrived, was also found inside the facility.
“When officers arrived they found a very chaotic and active crime scene,” Craig McCartt, the deputy chief of criminal investigations said, adding that they believe the gunman used a rifle during the attack.
The FBI, which is assisting in the investigation A statement from FBI Indianapolis Special Agent in Charge Paul Keenan, said a shotgun was seized from the suspect in 2020 after his mother told authorities that he might try to get killed by a law enforcement officer.
The suspect was interviewed last April and “no racially motivated violent extremism ideology was identified during the course of the assessment,” Mr Keenan said.