Yale University is no longer in lockdown after lifting its security alert for the entire campus.
The university had been on lockdown following an anonymous call to police in which someone claimed their room-mate was en route to the university's Old Campus "with the intention of shooting people".
Police believe a phone call reporting a man was en route to Yale University's campus "with the intention of shooting people" may have been a hoax.
Yale University in New Haven, Connecticut, was lockdown following the security alert, with Yale, New Haven and state police among the forces who descended on the Old Campus in the hunt for the gunman.
New Haven Police Chief Dean Esserman said the anonymous caller, who is not believed to be a student, was the one making the threat.
Esserman said the FBI is using voice recognition software to try and determine the identity of the caller, who will then be arrested and charged.
"We're going to find the person who made that call, we're going to put handcuffs on the person who made that call," Esserman added.
Yale University said it has lifted its "shelter in place" and lockdown alert "with the exception of Old Campus and Calhoun College".
The Ivy League university wrote on Twitter:
No further details were given.
Police are going door to door at Yale University to search for a gunman on campus, a spokesman has warned.
Yale University urged students and staff to co-operate, warning, "When they knock on your door, a Yale police officer will slip their Yale ID under the door".
"Police may use keys, but they will identify themselves", the university website added.
Libraries and some public schools are also on lockdown as the search continues, New Haven Police Department spokesman David Hartman said.
New Haven Police Department received an anonymous tip off from a male caller that his room-mate was en route to the Yale University campus "with the intention of shooting people", a spokesman said.
Police spokesman David Hartman told reporters both the caller and the gunman have yet to be identified.
He told a press conference: "There has been no report of gunfire, there has been no report of injuries of anyone.
"We are interviewing [two] witnesses who did report seeing somebody on or near the university campus with a long gun ... either a rifle or a shotgun".
Read: 'Man with gun' at Yale University
Officers from the Yale Police Department, New Haven Police and Connecticut State Police are "actively searching for any gunman" on the scene at the university's Old Campus, Yale's website states.
Issuing a renewed alert, Yale University warns its students and staff that the lockdown continues, adding, "THIS IS NOT A TEST".
Anyone with information on the gunman have been urged to call the emergency services.
Yale spokesman Thomas Conroy told local newspaper the New Haven Register, “Everyone is following instructions they were given in these alerts".
The Yale alerts warning an emergency situation is in place are sent by email, text message and phone.
Everyone in our community receives these alerts ... Everyone is alerted in multiple ways,” he added.
Students at Yale University have been on break since Saturday and classes do not resume until 2nd December.
Yale University has warned its students and staff it remains on lockdown and they should continue to "shelter in place" if on campus.
"IF OFF CAMPUS, STAY AWAY", the university's website warns.
New Haven Police Department Lieutenant Jeff Hoffman confirmed to student newspaper Yale Daily News there has been no shooting or any injuries as police search for a gunman on Old Campus.
Yale Police Department and New Haven Police have blockaded a road near to the campus.
SWAT teams are reportedly assembling outside Yale University's Old Campus following the confirmed report of a gunman on campus.
Yale Daily News, the student newspaper, also reported that announcements have been broadcast in dorm rooms warning of the situation:
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