Media playback is unsupported on your device Media caption "They were about to start [the final exam] and the fire alarm started and they evacuated everyone," said one student

Students are returning to Harvard University after part of its campus was cleared amid a report of explosives.

Students were told evacuate a dorm, two classroom buildings and science centre at 09:00 (14:00 GMT) at the elite college in Cambridge, Massachusetts.

All have now been reopened after the university said no explosives had been found.

Final exams, which had been under way at the elite college, were cancelled in the affected buildings.

Harvard said earlier in a statement: "The Harvard University Police Department 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."

Hoax?

The campus was cleared "out of an abundance of caution", added Monday's statement.

Media playback is unsupported on your device Media caption Are America's frequent lockdowns at schools and colleges an overreaction to the threat of mass shootings?

Two law enforcement sources told CNN they believed the report of explosives to be a hoax.

It is the latest security threat to a US school in recent months.

In November, another Ivy League institution, Yale University in Connecticut, was locked down for nearly six hours following a report of an armed man, which was later found to be a hoax.

In February, a gunman was reported on the campus of the prestigious Massachusetts Institute of Technology. That alarm, too, later proved false.

Amid the ongoing threat of mass shootings at US schools, such alerts are an almost daily occurrence, though most turn out to be nothing.

A BBC investigation found that, just in the month between 9 November and 9 December, US schools or college campuses were placed on "lockdown" on at least 130 occasions.