The prestigious Princeton University in New Jersey was briefly locked down Wednesday after a report of an armed man on campus, authorities said, according to Xinhua.
Students at the university were asked to remain indoors, but police soon determined that there was no gunman, according to the university's Web site.
However, four juveniles with a toy gun were taken into custody, New Jersey State Police said on its Web site.
Princeton Borough and Township police have reopened the campus and continue the investigation.
Shortly before 11 a.m. eastern time (1500 GMT), a male with what appeared to be a handgun was reported near the vicinity of a dormitory.
The all-clear was issued at 11:25 a.m. (1525 GMT).