Mr Gahler's officer later identified her as Snochia Moseley of Baltimore County.
"We do not believe there is an additional threat anywhere to the Harford County community", he said. They advised people to avoid the area.
Maryland state police block the road that connects the industrial business park, where several people had been shot, in Harford County, Md, Thursday, Sept. 20, 2018. The shooter, reportedly a woman, is in custody and in a critical condition in hospital.
Hogan also said authorities were "closely monitoring" the situation.
The hospital has declined to say whether one of the patients is the suspected shooter.
The Rite Aid center, situated among warehouses in an industrial park, has almost 1,000 employees, company spokesman Pete Strella said. She described it as a support facility adjacent to a larger building.
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She shot her first victim outside, police said, before re-entering the building where she continued shooting.
The Maryland woman who killed three co-workers and injured three others before fatally turning the gun on herself was mentally ill, authorities said Friday.
Update (11:05 a.m.): Police have confirmed that multiple people have been killed in the shooting.
Rite Aid spokeswoman Susan Henderson says authorities are at the scene and the company is cooperating with the investigation.
Deadly shootings are common in the United States, where the right to bear arms is protected by the USA constitution. We have our businesses locked down, so we're closed.
Hartford County Sheriff Jeffrey Gahler said the woman, who was from nearby Baltimore, had been working as a temporary employee at the distributrion center.
She was already down when officers arrived and an officer moved her from the scene, not knowing that she was the shooter, he said. Agents from the FBI and the Baltimore office of the Bureau of Alcohol, Tobacco, Firearms and Explosives are also responding to the incident.
The attack comes almost three months after a gunman shot dead five staff members of The Capital Gazette, in Annapolis, Md., 59 miles from the Rite Aid distribution center.