Chief Tracy Stone said the shooting occurred after officers encountered a man with a gun in the 5200 block of Newton Street in Bladensburg.
He said the man was struck in the lower body and taken to a hospital in critical condition.
According to Stone, police were sent to the Newton Street address about 9:15 p.m. after a man with a gun was reported there.
It was not immediately clear what prompted police to open fire after encountering the man. Police said a handgun was recovered at the scene.
A woman who lives in the condominium development where the shooting occurred said she heard six to nine shots. Then she said, "the police started rolling up."
Afterward, she said, she saw the wounded man placed into an ambulance.
"There was a guy who got shot [who was] rolled into an ambulance," the woman said.
The development where the shooting occurred is in the 5200 block of Newton Street.
Bladensburg is a town of about 9,000 inside the Capital Beltway, near the District on the eastern side of Prince George's County.
The town has its own police, but the Prince George's County police were expected eventually to assume control of the investigation.