Three people were gunned down when a woman opened fire in a pharmacy distribution centre in the US state of Maryland. The shooter later turned the gun on herself, authorities said.

Officials said another three people were injured by the gunfire. The Harford Sheriff's Department has identified the lone suspect as 26-year-old Snochia Moseley from Baltimore County.

She was a temporary employee at the distribution centre for Rite Aid, a national pharmacy chain. Investigators believe the suspect had a work-related grievance, although a motive was not immediately clear.

Harford County Sheriff Jeffrey Gahler confirmed that there were “multiple wounded and multiple fatalities” as a result of the shooting at a press conference early Thursday afternoon.

The Harford Sheriff's Department had tweeted Thursday morning that the situation was "still fluid," telling residents to avoid the area. The department also noted that police had been dispatched to the shooting in Aberdeen.

The first shots were reported just after 9am at the “Liberty Support Facility”, which is a portion of the Rite Aid distribution centre.

Law enforcement officers did not fire any shots, Mr Gahler said during the news conference on Thursday.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives and the FBI Baltimore were at the scene. The FBI had described it as an "active shooter situation".

"FBI Baltimore is responding and assisting [Harford Sheriff's Department] with an active shooter situation," the agency tweeted.

Maryland Governor Larry Hogan said on Twitter he was "closely monitoring the horrific shooting".

He added: "Our prayers are with all those impacted, including our first responders. The State stands ready to offer any support".

In a subsequent tweet, Mr Hogan noted that the Maryland State Police Department had also arrived to the scene of the shooting.

Schools in Harford County, including Roye Williams Elementary and Church Creek Elementary School had been placed on lockdown, according to local reports.