It was not immediately clear whether anyone had been killed, and details of incident remained largely unknown as of 11 am EDT.
Maryland: Several people were shot on Thursday in Perryman, Maryland, near an Army facility, according to authorities.
It was not immediately clear whether anyone had been killed, and details of the incident remained largely unknown as of 11 am EDT (1500 GMT).
"The situation is still fluid," the Harford County Sheriff's Office wrote on Twitter, adding that officers were dispatched to the incident shortly after 9 am EDT (1300 GMT). The sheriff's office said it would brief reporters around 11:45 am (1545 GMT).
Agents from the Baltimore offices of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and the FBI were also responding, the agencies said.
Perryman is 34 miles (55 km) northeast of Baltimore. The area of the reported shooting includes a church and a business district. It is a few miles from the Aberdeen Proving Ground, a large Army facility where military technology is developed and tested, according to Harford County's website.
A witness told NBC's affiliate in Baltimore that the shooting appeared to have occurred at a Rite Aid distribution centre.
"There's a lot of police activity and ambulances and fire engines," David Graf, an employee at a nearby local automotive repair shop that was on lockdown, told WBAL. "There's not any way to get out of the area, so I can only imagine there's still someone they're searching for."
Governor Larry Hogan said his office was "closely monitoring the horrific shooting."
"Our prayers are with all those impacted, including our first responders," Hogan wrote on Twitter. "The State stands ready to offer any support."
The shooting occurred a day after a man shot and wounded four people, including a police officer, at a Pennsylvania court building before he was killed by police, according to Pennsylvania State Police.