Police in New Haven, Connecticut, said they were searching Yale University for a gunman on Monday after an anonymous caller claimed his roommate was headed to the Ivy League school's campus intending to shoot people.
No one was injured and no shots were fired, said New Haven Police Department spokesman David Hartman, who noted that witnesses reported seeing a man on the campus with a "long gun," or rifle of some kind.
The department received an 911 call at 9:30 a.m. from a man on a pay phone near Yale's campus, who stated that his roommate was en route to the Yale University campus "with the intention of shooting people," Hartman told reporters.
"We have not yet identified that caller," Hartman said. "He did not identify himself when asked, he did not remain on the 911 line when asked."
Police shut down several blocks around the school, located in downtown New Haven, 80 miles northeast of New York City.
The school on its website told students and staff to shelter in place during the search.
"We've notified our community," spokesman Tom Conroy said, adding that warnings about the incident had been sent to students, faculty and staff by e-mail and text.
Televised images showed police officers responding to a largely deserted campus, as most students had gone home prior to the Thanksgiving holiday. New Haven and Connecticut State police responded to the scene, Yale said.
Some 11,250 students attend the prestigious university.
Institutions across the United States remain on high alert in the wake of a series of shootings including the attack at Los Angeles International Airport this month where a 22-year-old man killed a security officer and wounded three others, and last year's massacre at a Newtown, Connecticut, grammar school in which a gunman killed 20 young children and six adults.