Security operatives cordoned off the affected buildings.

The Harvard University on Monday evacuated four buildings at the heart of its centuries-old campus in Cambridge, Massachusetts, after warning students of unconfirmed reports that explosives had been planted.

The Ivy League school said it evacuated the Science Centre, Thayer, Sever and Emerson Halls.

“Out of an abundance of caution, the buildings have been evacuated while the report is being investigated,” Harvard statement said.

Institutions across the Boston area have been on an elevated state of alert since the April 15bombing attack at the Boston Marathon that killed three people and injured 264.

The Harvard Campus Police, Cambridge Police and Massachusetts State Police, including the bomb squad, responded to the campus, where they set up yellow-taped perimetres around the evacuated buildings and directed students to move away.

University officials closed Harvard Yard, the wooded and snow-covered historic centre of the campus to outside pedestrians, allowing only people who held Harvard identification to gain entrance.

People could be seen walking calmly outside the campus. The school, founded in 1636, has about 21,000 students.

Harvard’s campus is located in a densely populated urban area adjoining Boston. Students this week were scheduled to take final examinations.

Institutions across the Boston area have been on an elevated state of alert since the April 15bombing attack at the Boston Marathon that killed three people and injured 264.

“I’ve been here eight years and we’ve had a couple of one-off incidents, but nothing of this scale,” said Travis Lovett, 33, of Wakefield, Massachusetts, who works at Harvard.

It was the latest in a series of security scares at U.S. schools and universities. Three days ago a Colorado high school student intent on confronting a teacher opened fire at his school, severely wounding a classmate before killing himself.

Late last month, Yale University in New Haven, Connecticut, placed its campus on lockdown for most of a day, after an anonymous caller warned officials that his roommate was headed to the school planning to shoot people.

No gunman was found and police now regard the incident as a hoax.

(Reuters/NAN)