State Police troopers help investigate bomb threats to buildings at Harvard on Monday. (Photo: Massachusetts State Police)

There were campus emergencies on both sides of the Charles River on Monday, with Harvard evacuating students from four halls a little after 9 a.m. and locking down Harvard Yard because of unconfirmed e-mailed reports of explosives in each and the University of Massachusetts at Boston evacuating a building after reports of a person wielding a gun.

Harvard Resident Dean Jasmine Waddell talks with students waiting out a bomb threat evacuation in Annenberg Hall. (Photo: Stephanie Mitchell, Harvard staff photographer)

By 11 a.m., searches had found no explosives in the Science Center or Thayer, Sever or Emerson halls at Harvard, and students who remained evacuated were wondering when their missed final exams would be made up, according to reports in The Harvard Crimson.

By 12:56 p.m., Thayer and Emerson Hall were cleared for returning students and some were grumbling about the scare being the result of a student unprepared for a test. (When final exams were canceled, some students “erupt in applause,” the Crimson tweeted.) The final clearances came at about 2:45 p.m. But after recent terrorism and random school assaults, officials could not take chances. Harvard’s official statement:

Out of an abundance of caution, the buildings have been evacuated while the report is investigated. Harvard’s focus is on the safety of our students, faculty and staff. We will update the media when we have more information.

Cambridge Public Schools responded as well, with the nearby Baldwin School and Cambridge Rindge & Latin School “placed in a secure and hold mode as a precaution,” officials said, meaning recess was to be held indoors at the Baldwin and lunch is on campus at the high school. “Also. no unknown individuals are allowed into the buildings and all doors remained locked,” officials said. “All other activities within the school continue.”

The alarm in Boston went out shortly afterward, with UMass Boston tweeting at 11:55 a.m. to alert its community that they were to evacuate its McCormack Building while law enforcement gathered to deal with a “possible person with a firearm.” At 12:27 p.m., the report was cleared, with State Police calling it a “false threat” but clarifying that the four Harvard buildings remained evacuated while the search for possibly explosives went on.

When the situation at Harvard remained unresolved at 12:15 p.m., the Crimson tweeted that the Department of Homeland Security had joined State Police and the Harvard and Cambridge police departments at the Harvard Square campus “as threats of explosives remain unconfirmed.”

When shortly after noon the Harvard Square Business Association incongruously sent out a peaceful image of the square at dusk with the label “It’s beginning to look a lot like Christmas!,” resident Saul Tannenbaum responded on Twitter: “Except for the bomb squads and SWAT teams, sure.”

Update on Dec. 17, 2013: Harvard sophomore Eldo Kim, 20, is accused of sending “several” e-mailed bomb threats to avoid taking a final exam, trying to hide his identity by using the Internet router Tor. The FBI affidavit is here, via CBS News.