The bomb scare was speculated at four different sites inside the university campus, but the sites were later opened as federal and state officials did not find any explosives.

"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," a message on the University's website read.

"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," it said.

Later, in an update on its website at 2:44pm EST, the university said, "Science Center cleared. Students, faculty, and staff should enter through Science Plaza doors. All four sites now open."

Earlier, the Science Center remained closed while Sever Hall, Thayer and Emerson Hall were cleared besides the Harvard Yard. The university had said the report of bombs on campus remained unconfirmed. Federal and state officials have joined the probe, it added.

Authorities with Cambridge Police Department and school officers descended on four sites at the Ivy League school that included its science centre and freshman dorms. "Alert: Unconfirmed reports of explosives at four sites on campus," the school said in a Twitter message.

"HUPD and CPD are on the scene and investigating," read another tweet. Students, faculty and staff were sent e-mails and text messages, alerting them to evacuate the buildings shortly after 9 am (local time), a media report said.

The Harvard Crimson, the school's daily newspaper, tweeted that students erupted in cheers when officials announced that final exams scheduled for the day had been cancelled. Sever Hall is a red-bricked building erected in the late 1800s that houses classrooms and lecture halls. Thayer Hall is a student dorm.

The Science Center houses dozens of laboratories for multiple subjects, including astronomy, chemistry and physics. Emerson Hall, erected in 1905, serves as the home of the school's philosophy department. State troopers from the K9 and bomb squads have responded to the scene, Massachusetts State Police said.

The scare at the prestigious Harvard comes less than a month after Yale had a four-hour lockdown after an anonymous caller said his roommate was planning to shoot people on the campus. It also comes three days after an American schoolboy opened fire and wounded two fellow students before killing himself at a Colorado high school.

A classroom building was also briefly evacuated at the University of Massachusetts-Boston that has 16,000 undergraduates and graduate students, also taking final exams this week.

According to school spokesman DeWayne Lehman, university police got a call from someone who said they had seen a person with a gun in the building. The building was closed while university, Boston and state police searched it but said there was no one with a gun and the call is being investigated.

The main campus of the school, among the nation's most prestigious, sits on 210 acres in Cambridge. Harvard's student body includes about 6,700 undergraduates and another 14,500 graduate and professional students.

Harvard, founded in 1636, has educated current and former leaders from all over the world, including a long list of American presidents like Barack Obama and John F Kennedy.

 (Agencies)

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