URGENT: Possible Gunman Loose on the University of South Florida's Tampa Campus, School on Lockdown

Armed intruder in the library on the campus of the University of South Florida's Tampa campus. Students are being told to stay inside and lock their doors.  In an off-campus call transferred to USF police from the Hillsborough County Sheriff's Office, a person reported that a man with a gun was in front of the university's library, USF police Lt. Meg Ross said.

Officers have been on scene since about 1:43 p.m. and have not seen a person with a gun. Police are still securing the scene. Asked whether police thought the call was credible, Ross said, "You have to take them all seriously. We are on scene, and we're in the library now." Ross said she didn't have any information about who placed the call.

UPDATE#1: Two males detained.

Still developing. More to follow......