Doug Stanglin, USA TODAY
Police, responding to reports of an armed man in a residence hall, swarmed onto the campus of Central Connecticut State University Monday and arrested a man wearing camouflage pants after an intense search.
"The suspect is in custody, " New Britain Mayor Tim O'Brien said in a brief meeting with reporters.
The three-hour lockdown was lifted at 3:15 p.m.ET.
At around noon, the school had ordered students to remain in their dorm and away from their windows starting around noon.
"Remain inside building. Stay in Place! Stay away from windows. Police are on the scene," the university is telling students staff and faculty on its website.
The school told students via Twitter to "keep quiet, and put your cell phones on silent or vibrate."
NBC Connecticut ran a still photograph of police leading a black male, wearing an orange t-shirt and camouflage pants, in handcuffs.
Mark McLaughlin, spokesman for the university in New Britain, Conn., said, "Somebody was seen either with a gun or was thought to have a gun."
Officials stressed that this was not an active shooter situation, but is an "campus emergency."
Jordan Governale, a 20-year-old junior from Farmington, said he walked by a man carrying a backpack and with a sword and sheath strapped to his back. The man was wearing a mask, camouflage pants, knee pads and a vest resembling body armor, Governale said.
A minute later he said he saw police responding.
"At first I thought it was a Halloween costume. But after I saw the cops I thought it was some sort of threat," he said. "It's pretty scary. It's pretty strange, unexpected."
Mayor Tim O'Brien spoke briefly with reporters, saying only that police were "working diligently." He would not elaborate on the nature of the emergency.
More than 12,000 students attend the university outside Hartford, which has a 182-acre campus.