Another shooting in Tennessee.

Authorities said one person was killed in a mass shooting at a grocery store in Collierville, Tennessee, while a dozen others were injured.

Police are investigating the shooting as a possible workplace-related violence. Kroger officials did not immediately respond to questions about the suspected shooter's work status.

The suspected gunman died from an apparent self-inflicted gunshot wound at the store, authorities said.

Collierville Police Chief Dale Lane said 12 of the victims were rushed to hospitals.

Five of the victims were in critical condition, while one has been discharged, hospital staff told ABC News.

Terrified grocery customers, including children, ran from the building as gunshots erupted from inside the store, survivors and eyewitnesses said.

An employee said she was working in the grocery store's produce section when she heard five loud pops she thought were the sound of a co-employee busting balloons.

"I thought she was popping a lot of balloons... I looked up and see people running," the employee said.

Another employee said he heard women screaming in the parking lot about a gunman. He said he heard 10 to 15 shots from the grocery store.

"We found people hiding in freezers," Lane said. "They're doing what they had been trained to do -- run, hide, fight."

One worker fled to the grocer's roof and was escorted to safety by police.

The cashier said the gunman barged in the store, shooting. "He shot one of my co-workers in the head and shot a customer in the stomach."

The cashier added the gunman then left but continued firing his weapon.

Police from neighboring districts arrived at the Kroger grocery store to help secure the area.

"It breaks my heart to have to stand before you today... it's the most horrific event that's happened in Collierville's history," Lane said at a news conference following the incident.

A vehicle believed to owned by the gunman is still in the car park, Lane said. Authorities are awaiting equipment in order to safely inspect the vehicle, he said.

Police did not disclose the identities of the gunman and the victims, citing an ongoing investigation.

Last month, a gunman barged into a building and shot three employees of a company that makes plastic teeth aligners in Tennessee. Police killed the shooter.