The bell tower is seen on the University of North Carolina at Chapel Hill campus in 2014. Getty Images

UPDATE: 9:25 a.m. EDT -- The university issued an "all clear" Wednesday about 20 minutes after starting up emergency sirens while police investigated unconfirmed reports of an armed person near the NROTC Building and Venable Hall, which houses chemistry and marine science classrooms.

"The all-clear signal means the threat to the campus is over," it wrote on its Alert Carolina website, adding that students and staff should resume normal activities.

UNC Chapel Hill, located in Chapel Hill, North Carolina, has about 29,000 students. This year, three Muslim students were fatally shot at a nearby apartment complex by their neighbor over an alleged parking dispute. Craig Stephen Hicks was charged in the deaths of Deah Barakat, Yusor Abu-Salha and Razan Abu-Salh in what some have called a hate crime.

Original story:

The University of North Carolina at Chapel Hill activated its sirens Wednesday morning at about 9 a.m. EST due to police reports of an "armed and dangerous person on or near campus."

"The sirens are activated when there is a significant emergency or immediate health or safety threat to the campus community," the school's website states. "When the sirens sound, stop classroom and campus activities; all UNC operations are temporarily suspended. Remain inside your classroom or a safe place in your building unless police or University personnel instruct you to take a specific action, such as to evacuate a building, stay out of a certain part of campus, or go to your residence hall and stay there."