NEW BRITAIN, Conn. — An armed man was spotted today on the campus of Central Connecticut State University, prompting a schoolwide lockdown and warnings for students to stay away from windows as police SWAT teams swarmed the area.

The university declared a campus emergency and an hour later its website continued urging students to remain inside buildings.

It said police were searching in the area of a residence hall, and police officers were seen sheltering behind campus walls as several agencies responded.

University spokesman Mark McLaughlin said, “Somebody was seen either with a gun or was thought to have a gun.”

Jordan Governale, a 20-year-old junior, said he walked by a man carrying a backpack and with a sword and sheath strapped to his back. He 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.”

Lt. J. Paul Vance, a state police spokesman, says university police asked for assistance related to a report of a suspicious person.

More than 12,000 students attend the university outside Hartford, which has a 182-acre campus.