Officers received a call about an active shooter shortly before 6 a.m. at 1675 Airport Road in Kennesaw, Georgia. FBI bomb technicians and agents from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives also responded.
The male suspect was found dead from a gunshot wound inside the FedEx facility with a weapon, Cobb County police said. The wound appeared to be self-inflicted. Police believe he is the sole suspect.
The gunman was also carrying explosive devices that weren't used, police said.
Six victims were transported to Wellstar Kennestone Hospital, including one in critical condition, police said.
The building was secured and officers swept the area for unusual or suspicious devices.
FedEx spokesman Scott Fiedler told WSB-TV that the public does not have access to the facility.
"This incident happened at a FedEx Ground Hub – where packages are sorted and put on vans," Fiedler said.
FedEx clerk Liza Aiken told the Associated Press that she looked up and saw the man before he opened fire inside the package-sorting station. He was armed with an assault rifle, a knife and had bullets strapped across his chest "like he was Rambo," she said.
ABC News and The Associated Press contributed to this report.