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 9.30am local time yesterday from a man at a pay phone about 2km 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, Mr Hartman said.
There were no reports of shots fired or anyone injured.
Several local schools also were placed in lockdown.
The college is on November break, with undergraduate classes to resume on December 2. Many students and staff had left campus for Thanksgiving. Pedestrian traffic in the area also was sparse, with cold and windy weather keeping many people inside.
Police in tactical gear entered several buildings, and a helicopter hovered over the area.
Yale has been the target of violence in the past. In May 2003, a bomb damaged an empty classroom and adjacent reading room at the law school.
A Yale professor, David J Gelernter, was seriously injured in 1993 when a mail bomb mailed by Theodore Kaczynski, the man known as the Unabomber, exploded in his campus office.