The Administration Building and surrounding areas were evacuated.
Authorities say there's no sign of a gunman and no report of any shots fired as they searched a University of Arizona building floor-by-floor Friday night.
A text alert was sent to students and staff at 5:07 p.m. Friday saying police had received a 9-1-1 call about a man with a rifle inside the Administration Building.
"We are still assessing the situation," University of Arizona police Officer Joe Bermudez said. "We have patrol units on campus and we're working with Tucson police."
Campus police spokesman Sgt. Juan Alvarez says it's too early to say the report of a man with a gun is a hoax and authorities "are still treating it as a viable threat."
The Administration Building and some surrounding buildings near the campus's central mall were evacuated. Streets leading to the Administration Building were blocked, and dozens of police officers were seen on campus with a helicopter hovering overhead.
KOLD-TV reported that streets leading to the Administration Building were blocked off and dozens of police officers -- some wearing armored vests -- were seen on campus with a helicopter hovering overhead.
The campus has not been locked down.
A shooting at the University of Arizona's nursing school in October 2002 left three professors dead before the gunman killed himself.