The gunman, a 22-year-old day-shift employee, walked into the facility in Nashville neighborhood of Antioch just before 6 a.m. during a change of shifts and shot three people, the Metropolitan Nashville Police Department said.
A worker who witnessed the shooting told CNN she had just clocked in and sat down at her station when she saw the gunman, weapon in hand.
“I immediately started taking cover,” Charlotte Jennings, 53, told CNN by phone. She said she saw him raise the gun and remembers him saying, “Why you running?”
At that point, he pointed the gun and started “spraying the place” with gunfire, she said.
Police officers who were called to the site eventually encountered the gunman, who directed a semiautomatic pistol at them after being told to drop his weapon, police spokesperson Don Aaron said. Police then shot the gunman, Aaron said.
Earlier, police said the gunman had shot two people.
A fourth person injured her ankle while running, Aaron said.
The pistol had an extended magazine, Aaron said. No names were immediately released. Police also have not commented about a motive.
‘The shots lasted so, so long’
The shooting seemed to last for a long time, Jennings said.
“The shots lasted so, so long,” she said. “He let off a lot of gunfire.”
At some point, Jennings and others ran out a nearby exit.
“I never thought I would experience it on my job,” Jennings, a lifelong Nashville resident, said. “It was terrifying. I’m traumatized. It was just so scary.”
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The Antioch neighborhood is about a 12-mile drive southeast of downtown Nashville.
CNN’s Carma Hassan contributed to this report.