Harvard University ordered an immediate evacuation on Monday over unconfirmed reports of explosives at four sites on the campus of the elite university in the northeastern United States.
An alert on its website said there were unconfirmed reports of explosives at the Science Center, Thayer, Sever, and Emerson buildings. "Please evacuate those buildings now," it said.
The incident comes less than a month after Harvard's great rival Yale went on a four-hour lockdown after an anonymous caller said his roommate was planning to shoot people on the campus.
Harvard, one of the most prestigious universities in the world, dominates the Massachusetts town of Cambridge near Boston.
Harvard University and Cambridge police were on the scene and investigating, the university said on its website.