An investigation has been launched into the origin of an unsubstantiated bomb threat at Harvard Monday.

Schools officials announced early Monday afternoon that the administration had received a threat via email. In response, the university evacuated people from the four targeted buildings in and around Harvard Yard — including the Science Center, philosophy building Emerson Hall, visual and environmental studies building Sever Hall and freshman dormitory Thayer Hall — as national and local security officials searched the area. Katie Lapp, Harvard executive vice president, said law enforcement determined that the four buildings were safe and confirmed at 5:40 p.m. that the bomb threat was a false alarm. The source of the threat has not yet been identified, Cambridge Police Department spokesman Jeremy Warnick said.

“In lieu of the recent tragedies in Paris, Beirut and other parts of the world, I feel like this threat weighed deeply on a lot of people. Many of my peers and myself included got calls from concerned friends and family members,” Harvard sophomore Chris Zhang said. “I personally was not too scared of the threat itself, simply because threats like this one have happened in the past, but just the fact that something we’ve seen on the news could possibly happen so close to home was definitely concerning.”

Harvard University Police, the Cambridge police and fire departments and officials from the Department of Homeland Security, the Federal Bureau of Investigation and the Massachusetts Bay Transportation Authority arrived on campus following the threat. Officials searched both the Yard and all four buildings, informing students that each building was safe over the course of the afternoon.

Students said Monday’s evacuation reminded them of a similar threat made two years ago.

In 2013, Harvard student Eldo Kim issued a bomb threat that forced students to evacuate the same four buildings. He emailed Harvard officials, an HUPD associate and the Harvard Crimson president with the threat half an hour before he was scheduled to take a final exam.

Some students said in light of the similarity between the two threats, they were not overly concerned about the severity of Monday’s incident.

“Nobody was really worried, especially since apparently the buildings that were called in are the exact same ones Eldo Kim called in with the last bomb hoax,” Harvard sophomore Mack Andrews said. “I feel like almost everyone feels that it’s a hoax.”

Though students said a number of afternoon classes were cancelled after the alerts began, Faculty of Arts and Sciences Dean for Administration and Finance Leslie Kirwan sent an email to faculty encouraging them to hold classes in Sever and Emerson halls after police cleared the buildings later in the afternoon.

Harvard student Henry Tsang was among the students who had a class cancelled that afternoon. Tsang said students circulated a number of emails through campus mailing lists to offer freshmen — the primary residents of the buildings in close proximity to the Yard — spaces in upperclassman houses to relax, hang out or do work.

Yale Chief of Police Ronnell Higgins said the Yale Police Department was in contact with the Harvard Police Department throughout the day and they continue to monitor the situation.

In 2003, a bomb threat shut down a street adjacent to the Yale Bowl on the day of the annual Harvard-Yale football game.