A man has been charged with murdering three colleagues at a Maryland machine shop.

The alleged gunman, Joe Louis Esquivel, 23, of Hedgesville, West Virginia, was treated in hospital following a shootout with police and is currently being held at the Washington County Detention Centre.

Authorities say Esquivel arrived on Thursday morning for his normal shift at Columbia Machine in the small rural community of Smithsburg in western Maryland.

He allegedly worked until he left the building to retrieve a weapon, went back inside and fired at employees in the area of a break room.

Police responded to a 911 call at about 2.30pm.

It is not known what the motive of the attack was.

Police who arrived first on the scene found an injured person outside the business. As more police arrived, three bodies were located inside.

Esquivel, who is also charged with attempted murder and other offences, is said to have left the scene in a car but was quickly met by Maryland State Police.

A Maryland state trooper who was injured in a shootout with the suspect was treated in hospital and discharged late on Thursday.

The 25-year veteran of the Maryland State Police was shot when police said Esquivel fired multiple rounds at troopers. At least one trooper returned fire, striking the suspect, state police said.

A search warrant was executed at the suspect’s West Virginia residence, and additional firearms were located, the sheriff’s office said.

Washington County Sheriff Doug Mullendore identified those killed in the shooting as Mark Alan Frey, 50, of Hagerstown, Maryland; Charles Edward Minnick Jr, 31, of Smithsburg, Maryland; and Joshua Robert Wallace, 30, of Hagerstown.

Nelson Michael, the father of Brandon Michael, 42, who was injured in the machine shop shooting, said his son was still in hospital on Friday but he did not know more about his condition.

“He’s surviving,” he said. “I’m glad he’s alive, but it’s going to work on his nerves. I know that.”

Mr Michael said he did not know why the gunman shot the victims.

He added: “I’m just glad my son’s alive, and I feel so bad for the families of the other ones.”

Authorities said the investigation is ongoing.

Mr Mullendore said the suspect used a semiautomatic handgun, which was recovered after the shootout.

Smithsburg, a community of nearly 3,000 people, is just west of the Camp David presidential retreat and about 75 miles north-west of Baltimore.