The shooter was Andre Bing, an employee since 2010 who held a supervisory position as “overnight team lead”, Walmart said Wednesday. Bing opened fire on his co-workers in the break room of the store in Chesapeake, Virginia, according to the Associated Press, which cited a Walmart employee who was a witness.

Three bodies, including Bing’s, were found in the break room, the city of Chesapeake said on its Twitter page. Another was found towards the front of the store. Three others were taken to local hospitals but died of their injuries. At least six other victims were hospitalised and remain alive, including one who is in critical condition.

The Chesapeake killings add to a grim list of high-profile shootings that have erupted just before the Thanksgiving holiday. Five people were killed over the weekend at a nightclub in Colorado Springs, Colorado. Earlier this month, three members of the University of Virginia football team were killed in Charlottesville by a former player.

Walmart said it was working closely with authorities and vowed “to do whatever it takes to support our associates and Chesapeake neighbours” in the aftermath of the attack.

“We feel tragedies like this personally and deeply,” John Furner, head of Walmart’s US operation, said in a message to employees. “But this one is especially painful as we have learned the gunman was a Walmart associate. The entire Walmart family is heartbroken.”

More than 600 mass shootings have occurred this year in the US, according to Gun Violence Archive.

In Chesapeake, the shooter used a pistol and appears to have acted alone, Chief of Police Mark Solesky said at a media briefing. Bing was 31, according to the city, which is located in southeastern Virginia near Norfolk and Virginia Beach.

The attack happened less than an hour before the Walmart Supercenter store was due to close, said Leo Kosinski, a police spokesperson. The first call to 911 was received at 10.12pm, Solesky said. Responding police officers arrived two minutes later and entered the store two minutes after that, he said. Bing was found dead at the store.

The Bureau of Alcohol, Tobacco, Firearms and Explosives said on Twitter that its officers were on the way to Chesapeake to assist the investigation.

The Virginia attack once again thrusts Walmart deeper into the debate over US gun laws and mass shootings. A little more than three years ago, 23 people were killed as they browsed in a Walmart store in El Paso, Texas, during the back-to-school shopping season.

A further 26 people were injured in that attack, which prompted the retailer to curtail ammunition sales and stop selling handguns in Alaska, the only state where it still offered them at the time.

(With assistance from Maria Luiza Rabello.)