image source, WREG-TV/ CBSimage captionPolice and medical helicopters have landed at the scene of the shooting

Police in the US state of Tennessee say that one person has been killed in a mass shooting at a grocery store, and 12 other people have been wounded.

The attack took place in Collierville on Thursday afternoon about 35 miles (56 km) east of the city of Memphis.

Police from neighbouring districts have arrived at the Kroger grocery store to assist in the investigation.

The shooter, who is male, died at the scene from a suspected self-inflicted gunshot wound.

"It breaks my heart to have to stand before you today," said Collierville Police Chief Dale Lane in a news conference after the shooting. "It's the most horrific event that's occurred in Collierville history."

A vehicle believed to belong to shooter is still in the car park, Chief Lane said. Investigators are awaiting more equipment in order to safely inspect the vehicle, "as well as some property that's on him".

Some of the twelve wounded have suffered "very serious injuries" he said, and one died at the scene.

Swat officers went "aisle to aisle, room to room, clearing, bringing employees out that were in hiding", he continued.

"We found people hiding in freezers, locked offices," he added. "They did what they had trained to do – run, hide, fight."

Police have not identified the attacker, or given any possible motive. They are checking reports that he may have been a Kroger employee.

Glenda McDonald, who works in the Kroger's flower department, told USA Today that she "just ran out the door" as soon as she heard the first gunshot.

"I left my purse, my keys, everything," she said, adding that she saw a grocery bagger and a customer get shot.

Multiple ambulances and helicopters are on the scene to transport the wounded to a nearby hospital.

The active shooter alert triggered a brief lockdown at the nearby Collierville High School. The lockdown has since been lifted.

This is not the first mass shooting at a grocery store in the US this year. In March, a man attacked people at a supermarket in Boulder, Colorado, killing 10 people including a police officer.