State troopers, Lafin Borough officers and Luzerne County Sheriffs cruisers quickly surrounded the building along Route 315 after dispatchers received 911 calls that a teacher had seen a stranger walking in the halls.
That teacher told investigators that the man appeared to have a gun holster under his jacket and that he ran off when he was approached.
Luzerne County Assistant District Attorney Sam Sanguedolce described the man in question as six-foot tall, caucasian and heavyset, unshaven and wearing glasses, a fleece jacket and dirt-covered jeans.
"Police were there within minutes and had the place locked down,” said Sanguedolce. "The person left peacefully and we were unable to get which direction he fled, because he was gone by the time police responded. The teachers stayed in the building with the students."
Sanguedolce said Head Start and Luzerne Intermediate Unit students attend classes inside the seminary.
A state police helicopter aided in the search but authorities were unable to find the man.
Investigators said it is unclear if the man had a gun or how he got inside the seminary.
Anyone with information about the incident is urged to call the Laflin Borough Police Department at 570-654-3322.