(CNN) -- Princeton University ordered the evacuation of its campus for some eight hours Tuesday after "a bomb threat to multiple unspecified campus buildings," the school said on its website.
Princeton police dispatcher Kenneth Bruvik told CNN that the campus was evacuated because of an "emergency" but declined early on to give details.
"Please evacuate the campus and all university offices immediately and go home unless otherwise directed by your supervisor," the school's website message said. "Do not return to campus for any reason until advised otherwise."
Princeton University Spokesperson Martin Mbugua later told CNN, "The bomb threat was a phone call made directly to the university."
He said origin of the call had not been determined.
The campus was reopened at 6:25 p.m., after a sweep of buildings turned up no explosive devices, according to a statement from the university.
The university noted in a tweet during the evacuation that regular classes are over and commencement was last week. "Most students left campus days or weeks ago," the Twitter message said.
Students still at the university found places in the area to hunker down until it was OK to return to campus, according to Brianna Gagnon at the Yankee Doodle Tap Room. A pair of basketball players strolled in, and two dozen students congregated at the bar, she said.
At the Ivy Inn bar, part-owner Jeff Aton said that "there are not a lot of kids on campus for the summer," but "everybody who's there is being told to leave campus."
He said was not a big outflow of people from the school.
Emily Whitaker was one of more than 70 students holed up at the Princeton Public Library, which opened its doors to students and faculty looking for a place to go following the evacuation.
"To be honest it was scarier than I thought," Whitaker told CNN.
"It's very safe here. Princeton has always been such a safe place for all of us so this is strange" Whitaker said.
The Princeton sophomore is on campus for a summer theater program.
"I came out and all of the University library and the staff were flocking to the train. Blue lights were blinking everywhere, and the bells were ringing," she said.
The Princeton incident was one of several high-profile but apparently unrelated bomb threats that occurred Monday and Tuesday across the United States. One triggered a three-hour evacuation of Virginia's Richmond International Airport on Tuesday morning; another forced the evacuation of three state office buildings near Georgia's Capitol building in Atlanta, authorities there said.
A third, on Monday, led to a Texas-bound commercial jetliner being diverted to Phoenix after taking off from Los Angeles on Monday.