A man was seen being led away in handcuffs around 2:30 p.m.
New Britain Mayor Tim O'Brien said and CCSU reported on Twitter that one person was in custody. Lockdown was lifted around 3:15 p.m.
State police had been talking with a man who had been boxed into a dorm room in James Hall, a source told The Courant. There had been no hostile act, the source said.
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A number of floors in James Hall were evacuated during the investigation, a source said.
The CCSU campus was put on lockdown because of a "campus emergency" shortly after noon on Monday. Roads around the campus were closed. Classes have been cancelled for the rest of the day.
A spokeswoman at CCSU said the emergency was not a shooting but would not elaborate.
University spokesman Mark McLaughlin said that someone reported seeing an armed man on campus shortly before noon outside James Hall. McLaughlin heard that the man had a gun and a sword, but that information is not confirmed, he said.
He said there's been no report of an active shooter, no reports of injuries and no report of any hostages.
The incident began around noon Monday, when police activated a campus-wide alert telling students to get into the nearest building and "shelter in place," meaning lock doors, if possible, and to stay away from doors and windows.
"All on CCSU campus must seek shelter and stay indoors," reads a post from CCSU on twitter.com. "This is not a drill. Campus emergency."
Another tweet read "Seek shelter. Lock doors, close windows. We will communicate when we have more info. This is not a drill."
State police were called about 12:30 p.m. and have sent two SWAT teams, said Lt. J. Paul Vance. He said he does not know the nature of the emergency or where on campus police are focusing their attention.
SWAT officers were searching the campus, and there was no report of injuries, city police said at 1:10 p.m.
Around 1:13 p.m., police were seen speeding toward James Hall, a coed residence hall near the center of campus.
CCSU reported on Twitter around 2 p.m. that "there has been a report of a suspicious person carrying a gun on campus."
Nicholas Federici, a student and former police officer, said he saw a man with a sword and a handgun walking toward James Hall. The man was wearing green Army fatigues, black knee pads and some kind of mask, he said, and he was carrying a backpack that was "very full."
"I heard him drop his bag," he said — which made a noise he described as "a big thud."
Federici, a former police officer, followed from about 10 feet and called it in to police. An officer arrived quickly, he said.
New Britain Police Chief James Wardwell described the situation as "still very fluid" but did not elaborate. Police have set up perimeters around the campus and are asking that people not try to go to CCSU until the situation is resolved.
Newington is among the towns that also sent officers, police said. Officers have been sent to direct traffic, a dispatcher said.
West Hartford sent an officer with a "bear cat," a four-wheel drive, armored vehicle, and a second emergency services vehicle, said Lt. Chris Chappelle. The second vehicle was not used at the scene, he said.
Asked why there is a lockdown, Fernando Marroquin, spokesman for Mayor Tim O'Brien, said, "We're trying to figure that out."
O'Brien didn't offer many details when he first met with reporters at the scene.
"When we have information we will provide it to you. Police are on the scene and they are responding."
"Police are taking care to make sure the public is safe."
Paul Schlickmann, director of athletics at Central, said he doesn't know the nature of the emergency.
All he knows is that school officials "have told us to stay away from doors and windows."
Rachael Bentley, the managing editor of the campus newspaper The Recorder, said the campus was deserted soon after the alert was issued. Bentley said most of the police presence was near James Hall and the Central Square Plaza at the corner of Stanley Street and Paul Manafort Drive.
"Twelve o'clock on Mondays is the busiest time of the week. Everyone has classes," Bentley said. "The campus should be a beehive, and it's dead. There's no one around."
Bentley and other staff of the newspaper were locked in their office inside the student center. She said that student center staff members were posted at the doors and weren't allowing them to leave. Students in the student center are lined up and sitting against the wall.
She added that some students she knows learned about the news from Twitter and Facebook instead of the campus alert system.
Sal Marino from Middletown came to campus after hearing from his daughter, a student. She was in Willard Hall in a classroom, he said.
"I got a text from her telling me the school was in lockdown. They locked the doors and shut the blinds."
"I immediately left work to be here"
"She is very stressed and she is very anxious. She just wants to get out."
"It was an instant flashback to what we've seen in the past … hopefully it will turn out they reacted fast enough to protect everyone."
CCSU's website has been replaced with a page that reads: "Central Connecticut State University – Campus Emergency Get inside buildings & Stay in place! Stay away from Windows. Police are on the Scene."
Three nearby New Britain schools — Smalley Academy, Holmes Elementary and HALS Academy — are on modified lockdown, a school district official said.
The mother of one CCSU student who would not give her name said her son and his roommate was barricaded inside his James Hall dorm room with a bureau against the door. They didn't know what was going on, she said.
CCSU student Valenz Santana said he had heard reports of a man with a gun and a blade of some sort.
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