Bakner said the woman scrambled out of the vehicle and ran. The gunman jumped inside the Bronco and drove away, he said.
When authorities arrived, the woman refused medical treatment, Bakner said.
Police were looking for a black man in his late teens or early 20s. The man being sought was described as having a thin build and a medium complexion. Police said he was wearing a black coat.
Police said the vehicle, a 1985 Ford Bronco, is gold and green in color and had Virginia tags HALEE94.
Carjackings are not an every-day occurrence in Washington County, but police cautioned that neither are they unheard of.
"They occur occasionally, but not every day," Bakner said. "We get them. They do occur."
Police agencies that patrol Washington County said carjackings are not common.
Maryland State Police Sgt. Steve Jessee, of the Hagerstown barracks, said state troopers handle auto thefts but almost never get a call for an armed carjacking.
"As far as actual carjackings, I would say it's very rare," he said. "I don't recall us handling an actual carjacking. The only one that I can recall is the taxi cab in connection with that bank robbery."
In that instance, a passenger in a taxi cab ordered the driver and other passengers out of the cab at gunpoint and drove away. The cab was later used as the getaway car in a bank robbery.
Sgt. Tom Newton, of the Washington County Sheriff's Department, said deputies almost never have to investigate carjackings.
"Fortunately, we get about one every five years," he said. "Our five years is up, I guess. It's such a small community, people don't have an easy chance to get away."
For now, carjackings are far more common in larger cities like Washington and Baltimore, Newton said.
"I just hope it stays down in the city," he said.