Four juveniles are in custody after one was spotted with what appeared to be a gun — but turned out to be a toy — on the Princeton University campus, police said.

Princeton Borough authorities are questioning the children after the confusion that caused a lockdown at the Ivy League school was cleared up.

"The suspected handgun was determined to be a plastic handgun that was dark in color," the university said in a press release about the incident.

The New Jersey school's Web site and alert system advised people around 11 a.m. EDT to stay inside following a report of a male with what appeared to be a handgun near Dod Hall dormitory.

An all-clear was issued around 11:25 a.m. EDT, and Princeton's Public Safety Department said there was no gunman despite the earlier reports.

Police continue to investigate.

It was not clear how many students remained on campus because graduation took place on Tuesday.

The Associated Press contributed to this report.