The University of North Carolina in Chapel Hill, N.C. (AP Photo/Gerry Broome)

This post has been updated.

The University of North Carolina in Chapel Hill issued an “all clear” and lifted the shelter-in-place warning officials had issued Wednesday morning.

The flagship state university posted this warning shortly before 9 a.m.:

Emergency: The University has activated the sirens. Police report an ARMED AND DANGEROUS PERSON ON OR NEAR CAMPUS.

Go inside immediately.
Close windows and doors.
Stay until further notice.
Follow directions from emergency responders or University officials.

The alarm was raised after an anonymous, unconfirmed report of someone armed and dangerous near the campus ROTC building, a university spokesperson said. Police quickly blocked off the area but did not find anyone. The investigation is ongoing. The spokesperson could not confirm whether ROTC training at Carolina includes weapons.

Shortly before 9:30 a.m., officials announced that the lockdown was over.

It has been an anxious fall on many campuses.

Several colleges have locked down in the weeks after a student walked into a community college in Oregon and shot nine people to death. Protests on many campuses over racial and other bias issues have raised tensions, with death threats shutting down classes at Western Washington University last week and the University of Chicago on Monday.

Read more:

Man arrested for threatening to kill ‘white devils’ at the University of Chicago

A debate about mascots touches off racial tensions and a violent threat