A bomb threat at Harvard University led to evacuations of four university buildings on Monday, and final exams in the buildings were canceled or postponed. No explosives were found.

The police department at the Cambridge, Massachusetts, school said it had received an e-mail warning that explosives may have been planted at the heart of the campus in three buildings — the Harvard Science Center, Sever Hall and Emerson Hall — and the freshman dormitory Thayer Hall.

"Alert: Reports of bombs placed on campus are unconfirmed," the university wrote on its website, including Facebook and Twitter, just after 9 am. "There have been NO reports of explosions."

"Out of an abundance of caution, the buildings have been evacuated while the report is investigated," the Harvard emergency website wrote. "Harvard's focus is on the safety of our students, faculty and staff."

Fire alarms rang in each of the buildings and Harvard alerted it students with text messages at 9:08 am. By 9:33am, the university was posting regular alerts on its Web pages. By 2:44 pm, all four buildings and Harvard Yard where three of the four buildings are located had been cleared and students were allowed to return.

In addition to the campus police and Cambridge police, federal and state officials were at the scene for backup. President Barack Obama was briefed about the threat at his alma mater, Harvard Law School, a White House official said.

"All I hear are sirens," Krystle Lischwe wrote on Twitter. "I'm having horrible flashbacks… Be safe @Harvard!"

Those flashbacks were presumably of the chaos that erupted after the Boston Marathon bombings in April, which included a major manhunt and lockdown of the city.

"From the reactions of myself and other Harvard grad students, we are pretty sure this explosives business is a scheme to get out of exams," wrote Kimberly St. Julian on Twitter.

A picture posted on Facebook of Harvard President Drew Faust speaking with students in Annenberg Hall after evacuations were ordered drew a number of comments.

"It's one way to get out of final exams!" wrote Steve Angelique.

Each year, several bomb threats are phoned into various offices at the university offices, according to the campus police website.

In November, another Ivy League school, Yale University in New Haven, Connecticut, was locked down for about six hours while authorities investigated a phone call saying an armed man was heading to the school, which authorities later said was likely a hoax.

carolineberg@chinadailyusa.com