The University of North Carolina at Chapel Hill issued an "all clear" Sunday less than an hour after sending an emergency alert about an armed person. Police said the man was in custody.

The school activated its emergency sirens Sunday afternoon. Authorities also locked the doors to Carmichael Arena, site of an NCAA women's tournament game between the Tar Heels and the University of Tennessee at Martin.

Ever Castro, a junior, said he saw one man following another man and yelling at him, starting at the student union and continuing to the student dining hall.  Two other students tried to help the man being followed, he said.

"And then the man was following them even then, and he followed them almost all of the way back to the union and at that point, that's when I saw that he had the knives," Castro told The Associated Press.

Chapel Hill police caught the unidentified man off campus, and he was transferred to the custody of university police, a school spokeswoman said in a news release. No injuries were reported.

He had displayed a knife or knives while on campus near the Pit, a gathering area located near the student union, spokeswoman Karen Moon said.

Students and others on campus had been advised to close their windows and doors and stay inside while the alert was in effect.