Two victims were shot inside a car and the third died in the parking lot just before 10 am outside the store in Duncan, Police Chief Danny Ford said.

Authorities did not immediately describe a motivation for the shooting. Ford told The Associated Press that investigators believe the gunman shot the male and female victims and then turned the gun on himself.

Stephens County District Attorney Jason Hicks authorities said during the news conference Monday afternoon that there was never an active shooter inside the store and he described the shooting as an isolated incident. He did not further explain.

Hicks said the two victims had been inside the Walmart Money Centre, which offers check-cashing, money orders, tax preparation and other services, before they were killed, but that the shooter did not enter the business.

Two bodies covered with sheets were visible in the parking lot Monday afternoon. One body was in the driver’s seat of a red, two-door car. The other body was lying on the ground next to the vehicle.

Bullet holes were visible in the car’s windshield. Police said in a Facebook post that a handgun was found at the scene. At the news conference, Ford described the gun as semi-automatic but said he had no further details. He said the Oklahoma State Bureau of Investigation was still processing the scene.

Ford said he believed nine shots were fired.

Authorities have not released the identities of those killed but did confirm the shooter was among the dead. Ford said all three knew each other but declined to describe their relationships or other identifying information pending notification of immediate family.

He said all three were dead when police arrived just minutes after the shooting.

Walmart spokeswoman LeMia Jenkins initially said no staff were involved. Jenkins later released a statement offering thoughts and prayers for the family of the woman killed in the shooting, who she said had been with the company for less than two months. Jenkins said the woman was at the Walmart during her free time and wasn’t scheduled to work that day.

Duncan is a city of more than 22,000 residents located about 80 miles (130 kilometres) south of Oklahoma City. The Walmart is in a commercial centre that includes a sporting goods store and a dollar store along US Highway 81, the main road that passes through Duncan heading south toward Texas.

Aaron Helton, of Duncan, said he was parking outside the Walmart where he planned to buy groceries when he heard about nine gunshots.

“I arrived and there were three bodies,” Helton said.

Helton was one of many nearby witnesses who fortunately was not hit by gunfire, Ford said. The closest person was in a vehicle three parking spaces away from where the victims sat, Ford said.

“We got radio of a lot of people dodging and running,” Ford said. “There were people in the vicinity, for sure.”

There were more than 100 vehicles in the parking lot about two hours after the shooting plus a steady stream of customers coming and going from Walmart, which remained open for business.

It was at least the third shooting at a Walmart in the US this year. A Walmart store in El Paso, Texas, reopened Thursday after being closed since August, when a gunman opened fire in the busy store, killing 22. Just days before, two Walmart employees in Mississippi were killed by a man authorities described as a disgruntled Walmart worker.

The killings in Oklahoma come amid a spate of high-profile shootings across the US. A 16-year-old student at a high school in the city of Santa Clarita outside Los Angeles shot and killed two classmates and wounded three other teens Thursday before shooting himself in the head. He died the next day.

In New Jersey, players and spectators ran for cover Friday night when a gunman opened fire at a high school football game, wounding two people. And on Sunday, four people were killed and six wounded in Fresno, California, where police say two shooters sneaked into a backyard party and shot into a group of Hmong family and friends.