HARFORD • Three people were killed yesterday in an early morning shooting at a business park in Harford County, Maryland, in what appears to be a targeted attack, the authorities have said.

Two other victims were in critical condition, The Baltimore Sun reported.

The suspect has been identified as 37-year-old Radee Labeeb Prince, Harford County sheriff Jeffrey Gahler told reporters.

All five people shot were employees of Advanced Granite Solutions, a company in the Emmorton Business Park.

It is located about 32km north-east of Baltimore, with car body shops, hotels and storage units in the area, the Washington Post reported.

"This does appear to be a targeted attack, limited to that business," Mr Gahler said at a news conference, adding the case is still being investigated.

Police are hunting for the suspect who was armed with at least a handgun, and left the scene in a black vehicle.

The Washington Post reported that just before 10am yesterday, a woman frantically answered the phone "at a marble and tile supply store" and said she was hiding under a desk.

She said her boss was outside the store and could not get in because of the police activity.

"I'm not sure what's going on," she said before hanging up to take another call.

Mr Larry Hunt, the manager of RE Michel Company, a heating and air-conditioning parts business in the business park, said he and other employees were outside talking to a customer at about 9am when they heard loud arguing.

It sounded like it was coming from a business about half a block away, though he did not hear gunshot sounds, he said.