Florida State University (FSU) has brought its campus to a halt Thursday in the wake of a campus shooting that has left the gunman dead and three shot and injured.

According to the Associated Press, police have categorized the shooting as an "isolated incident," but did not know what the gunman's motive was. Authorities also did not provide much further detail after the fact.

The shooter, who was apparently an FSU student, walked into the school Strozier Library early Thursday morning and opened fire. Police shot and killed the gunman when he refused to lower his weapon and opened fire on them instead.

"This person just for whatever reason produced a handgun and then began shooting students in the library," FSU Police Chief David Perry said in a news conference some hours later.

FSU's library sits in the middle of the school's campus, which is located less than a mile from downtown Tallahassee and the state capitol. The school announced on its website that classes had been cancelled on Thursday, the library "closed until further notice" while the rest of campus is "otherwise fully operational."

Students inside the library when the attack started said they barricaded themselves behind overturned chairs, desks, offices and book aisles, while some bolted for the nearest exit. Of the three students who were shot, one was treated on the scene with a minor injury while the other two were taken to the local hospital.

"I ran for my life," Allison Kope, a freshman from Cocoa Beach, told the AP. "I ran right out the backdoor. My laptop and everything is still in there. It was shock. It was just instinct. You don't think about anything else, you just go."

According to Reuters, one of the two students taken to the hospital was in critical condition while the other was stable.

"The three students who have been injured are our highest priority," FSU President John Thrasher said in a statement.