An anonymous caller warned authorities that his roommate was on his way to Yale University to shoot people, leading officials to lock the Ivy League campus down as police searched for a gunman.
At least two witnesses reported seeing someone on or near campus with a long gun.
An emergency call was received around 9:30 a.m. local time from a man at a pay phone about two kilometres from the campus, said Officer David Hartman, a New Haven Police spokesman.
"All he really said was that his roommate was on his way to the university, to Yale University, to shoot people," he said.
Police later received reports from witnesses who reported seeing someone with a gun, Hartman said. He said that there was nothing specific about the threat and that the call lasted just several seconds.