The Harford County Sheriff’s Office confirmed the shooting near Spesutia and Perryman roads in Aberdeen. The first shots were reported just after 9 a.m.
It wasn't known if officials had taken anyone into custody in connection with the incident.
"We are closely monitoring the horrific shooting in Aberdeen. Our prayers are with all those impacted, including our first responders. The State stands ready to offer any support," Maryland Gov. Larry Hogan said.
The conditions of those injured weren't disclosed by authorities.
It wasn't immediately clear if the shooting occurred at a particular business or was out in the open. The area contains many warehouses.
“We can confirm there was a shooting in the area of Spesutia Road and Perryman Road. Multiple victims. The situation is still fluid. Please avoid the area,” the sheriff’s office tweeted.