Officers in riot gear searched a locked-down high school Friday after a student and his grandmother reported seeing someone put a handgun in a backpack and approach the building.

The two believe that person was another student but weren't been able to identify him inside the school building, and no gun was found after an hour of searching, officials said.

Leonardtown High School was locked down along with an adjoining middle school and two other campus buildings. Officials began dismissing students from the high school shortly after 1 p.m. and police planned a second search once the building was cleared.

"We want to let everyone know we are taking every precaution to keep the students, the staff and the community safe," County Sheriff David D. Zylak said. "We have no active shooter at this time."

Students were patted down and searched during the lockdown, Zylak said.

One girl was taken away by ambulance after suffering an anxiety attack, and two construction workers found behind the school were taken into custody on unrelated charges of illegal substance possession, County Sheriff David D. Zylak said.

St. Mary's County Public School system officials referred calls to county government officials, who could not immediately be reached by telephone. Calls to the middle school and adjoining technology center were referred to the central office.

Leonardtown is in southern Maryland, about 50 miles southeast of Washington.