(CNN) -- Four Harvard University buildings were evacuated and closed for hours Monday because of a bomb threat, prompting some classes at the Boston-area Ivy League school to reschedule or cancel final exams.
After evacuating three classroom buildings and a dormitory Monday morning, authorities found no suspicious devices and reopened all of them by 3 p.m., Harvard said on its website.
Final exams that were supposed to take place in the affected buildings Monday morning were canceled or postponed because of the report, student newspaper The Harvard Crimson reported, citing university officials.
Two law enforcement sources told CNN late Monday morning that the threat appeared to be a hoax.
The school said its police department received an e-mail, sent around 8:40 a.m., claiming that explosives may have been hidden in the three academic buildings -- the Harvard Science Center, Sever Hall and Emerson Hall -- and a freshman dormitory, Thayer Hall.
Harvard ordered the evacuations around 9 a.m., alerting students and staff by e-mail, voicemail and text messages.
"Safeguarding our community in this instance unfortunately required the disruption of exams and the evacuation of one of our freshman dormitories," Harvard Executive Vice President Katie Lapp said on the school's website. "(Harvard police), in close cooperation with local, state and federal agencies, is continuing to investigate this incident to determine who may be responsible."
All but the science center were declared safe by 2 p.m., according to the school.
Some students were taking final exams in the affected buildings when the evacuations were ordered, said student Sam Weinstock, incoming president of The Harvard Crimson.
At least some of the evacuees were taken to a freshman dining hall, where they were told their Monday morning exams would be called off, Weinstock told CNN.
Elsewhere on campus, Weinstock said, students were "more or less going about their days."
Harvard's final exams for the fall term began last week and are scheduled to go through Friday.
Students' instructions for what to do about missed exams, such as whether and when to retake them, appeared to vary by class. Instructors for a set of science classes told their students that they could take their exams Monday night or in February, or skip the test and accept a grade based on work done so far, the Harvard Crimson reported.
Roads around Harvard Square, the Cambridge commercial center near Harvard's campus, also were closed for part of Monday morning because of the threat. Cambridge police said the roads were reopened around 11 a.m.
CNN's Deborah Feyerick, Susan Candiotti, Alexandra Field and Shimon Prokupecz contributed to this report.