A shooter killed three people and wounded two others Thursday at a drugstore distribution centre in Harford County, Maryland, officials said.

A law enforcement official who had been briefed on the incident provided the casualty toll for CNN.

The fate of the shooter was not clear. The shooting occurred at a Rite Aid support facility about 30 miles northeast of Baltimore.

“What I understand is the location is secure,” said Rite Aid spokeswoman Susan Henderson. Roughly 1,000 employees work there.

“The distribution center is where products are received and processed for delivery,” she said. “The shooting happened adjacent to the primary building.”

People were being asked to avoid the area just outside the city of Perryman. Homes, churches and a cemetery are in the vicinity. Railroad tracks run alongside a business park.

The Bureau of Alcohol, Tobacco, Firearms and Explosives sent agents from Baltimore. The FBI's Baltimore office is also assisting.

“We are closely monitoring the horrific shooting,” Gov. Larry Hogan tweeted. “Our prayers are with all those impacted, including our first responders. The state stands ready to offer any support.”

This marks the third mass shooting in the country in the span of a day.

A shooting at an office complex in Middleton, Wisconsin left three people injured Wednesday, and a gunman injured four people at the Masontown Borough Municipal Center in Pennsylvania later in the day.

Police killed the shooters in both Wednesday incidents.