UPDATE: Harvard University has announced all four sites have been cleared for potential explosive threats and students may return to campus.
Harvard University has ordered a mass evacuation following unconfirmed reports of explosives at four sites on its campus outside Boston.
A notice was posted on the emergency section of the institution's website ordering Science Center, Thayer, Sever, and Emerson to be evacuated, while the university's Twitter account issued alerts.
The institution reiterated there had been no reports of explosions.
Alert: Unconfirmed reports of explosives at four sites on campus: Science Center, Thayer, Sever, and Emerson. Evacuate those buildings now.— Harvard University (@Harvard) December 16, 2013
Alert: HUPD and CPD are on the scene and investigating. Stand by for more info. View emergency page for updates http://t.co/VAZ1odRYB9— Harvard University (@Harvard) December 16, 2013
Alert: Reports of bombs placed on campus are unconfirmed. There have been NO reports of explosions. View for updates: http://t.co/gAWVUFoPtp— Harvard University (@Harvard) December 16, 2013
A statement on the university's website read:
"The Harvard University Police Department (HUPD) this morning received an unconfirmed report that explosives may have been placed in four buildings on campus: the Science Center, Thayer, Sever and Emerson Halls.
"HUPD and Cambridge Police are on the scene. Out of an abundance of caution, the buildings have been evacuated while the report is investigated.
"Harvard's focus is on the safety of our students, faculty and staff. We will update the media when we have more information."
Police confirmed they were attending the university, tweeting:
Complaints have already been made over the lack of information about evacuation procedures.
Harvard history student Gary Gerbrandt posted on the university's Facebook page: "How is the focus on the safety of students when the emergency announcement doesn't provide any instruction on how to evacuate or what the circumstances are? How can students stay safe when they are given no information by this administration?"
Cars have been prevented from accessing the roads surrounding the university's science centre, according to local journalists.
The university added: "Access to Harvard Yard has been restricted to residents of the Yard with Harvard ID. As of the writing of this message the report remains unconfirmed and the HUPD has no reason to believe there is a threat to any other site on campus."
Later that evening the university said all four sites had been cleared and students may return to campus. There have since been reports the incidents, which took place during students' final exams, were a hoax, CNN reported.
Katie Lapp, executive vice president of the institution, said federal agencies would be investigating who was responsible for the incident.
"[The evacuation] was taken out of an abundance of caution after an email was received at approximately 8:40 a.m. by the Harvard University Police Department and other community members, claiming that explosive devices may have been hidden at those four sites. I am relieved to report that no suspicious devices were found.
"I would like to thank the HUPD and the many representatives of the local, state and federal agencies who responded to this incident. We deeply appreciate your help in keeping our campus safe.
"Safeguarding our community in this instance unfortunately required the disruption of exams and the evacuation of one of our freshman dormitories. The HUPD, in close cooperation with local, state and federal agencies, is continuing to investigate this incident to determine who may be responsible.
"Please be assured that the safety of our students, faculty and staff is our top priority. At this time, we know of no specific threat to campus and activities are returning to normal."