An unidentified assailant opened fire Thursday at a warehouse complex north of the US city of Baltimore, killing and wounding multiple people, authorities said.
A lone suspect was in critical condition at a local hospital, according to Harford County sheriff Jeffrey Gahler.
Police would not confirm reports that the shooter was a woman, but revealed that the suspect had not been shot by police.
"I can confirm multiple wounded and multiple fatalities," Gahler said.
US media reported that three people were killed and two others wounded in the incident, which erupted around 9:00 am (1300 GMT) at a distribution centre for the Rite Aid drugstore chain.
Gahler said the assailant apparently was armed with a single handgun "and no shots fired by any officers responding to the scene."
"We do not believe there is an additional threat anywhere to the Harford County community," he said.
Deadly shootings are common in the United States, where the right to bear arms is protected by the US constitution.
Attacks by women are extremely rare, however, accounting for less than five percent of the total, according to studies.
Thursday's attack came five months after an Iran-born female animal rights activist gunned down three people before killing herself at YouTube's California headquarters.
Maryland made grim headlines around the world in June when five employees of Capital-Gazette newspapers died after a gunman stormed their Annapolis office.
The man police say is responsible had harassed the newspapers' employees for years over an article about criminal stalking charges against him, the Baltimore Sun reported.
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