WASHINGTON (AFP) - Princeton University ordered the evacuation of its New Jersey campus on Tuesday after receiving bomb threats to "multiple and unspecified campus buildings."

Students were alerted to the threat through university's emergency notification system, and instructed to "evacuate the campus and all University offices immediately" and not to return for any reason.

"There has been a bomb threat to multiple unspecified campus buildings," it said.

Emails carried the subject line "Princeton Alert - Bomb Threat - Evacuate!"

Regular classes are not in session at the Ivy League school in New Jersey due to the summer holidays but the campus is still sparsely occupied by students, faculty and staff, usually to conduct research.

Princeton's alert system has previously provided false alarms. In 2009, it reported the presence of a gunman on campus, but the threat proved to be a student carrying props for a play.