Armed police have been sent to the University of Exeter after a student reportedly made threats while holding a "handgun".
Students were evacuated from a building as police units with guns and dogs entered the campus on Wednesday afternoon.
Devon and Cornwall Police said no injuries were reported and are investigating whether the weapon is genuine.
"Armed units were sent to Exeter University following reports of a student making threats to other students, whilst in possession of a handgun," a spokesperson said.
"Police currently have one man in custody and have seized a weapon; we are now looking to see if this weapon is genuine or a replica.
"We can confirm that we have had no reported injuries and are not currently looking for anyone else in connection to this matter. We wish to reassure those on campus that they are safe. Local officers will remain in the area as we continue our enquiries into this incident."
One witness said she was in the Amory building, on the university's Streatham Campus, when people were ordered to leave.
"We were all shouted at to leave now, and came outside to police with guns," she wrote on Twitter.
A spokesperson for the University of Exeter said police were called immediately and "the incident was dealt with swiftly and effectively".
"As a precaution, one building was closed for a short period of time, this building has now been reopened and the campus has returned to normal," she added.
"The safety of everyone on campus is our overriding priority and the university has strict protocols in place for incidents of this nature. We would like to reassure those on campus that the incident is now over.”