"It obviously was premeditated," said Binghamton Police Chief Joseph Zikuski, noting the gunman blocked the rear exit with his car. "He made sure nobody could escape."
"We have very good reason to believe the shooter is among the dead," Zikuski said, reported the New York Times. Two handguns were recovered at the scene.
No motive has been identified.
The gunman, who is described in media reports as being of Vietnamese descent, entered a foyer at the American Civic Association and shot two receptionists, Zikuski said. One receptionist was killed, but another pretended to be dead, then crawled a desk and called 911. Police responded within two minutes.
The gunman entered a room near the reception area and continued firing, the chief said. He fired on a class on U.S. citizenship, Hinchey said.
"People were there in the process of being tested for their citizenship," Hinchey said in a telephone interview. "It was in the middle of a test. He just went in and opened fire."
Twenty-six people hid in a boiler room and 37 people were safely removed from the building, Zikuski said. Four people are in critical condition.
Emergency dispatchers were in contact with some people inside by phone, WBNG-TV reported. The Binghamton SWAT team responded.
Most of the people brought out of the building couldn't speak English, the chief said.
Zhanar Tokhtabayeva, 30, who is from Kazakhstan, said she was in an English class when she heard a shot and her teacher screamed for everyone to go to the storage room.
"I heard the shots, every shot. I heard no screams, just silence, shooting," she told the AP. "I heard shooting, very long time ... and I was thinking, when will this stop? I was thinking that my life was finished."
The gunman's connection to the center isn't clear, Hinchey said.
"One of the first questions is going to be, what motivated this?" he said. "What caused this to happen? What was the kind of person who did it?"
According to the Binghampton Press and Sun Bulletin, Broome Community College Assistant Professor Tuong Hung Nguyen, who is fluent in Vietnamese, was asked to work with police to communicate with the shooter.
The American Civic Association helps local immigrants with naturalization applications, according to U.S. Citizenship and Immigration Services. The association describes itself as helping immigrants and refugees with counseling, resettlement, citizenship, family reunification and translators.
It also intervenes with emergencies, including fighting, hunger and homelessness, according to information from the association's Web site.
The association's president, Angela Leach, "is very upset right now," said Mike Chanecka, a friend who answered a call at her home as Leach wept in the background, according to the AP.
"She doesn't know anything; she's as shocked as anyone," Chanecka said. "For some reason, she had the day off today. And she's very worried about her secretary."
Five people with gunshot wounds were being treated at Wilson Medical Center in Johnson City, a hospital spokeswoman said.
The shooting occurred in a mixed neighborhood of homes and small businesses in the center of the city.
Maryam Weisser, a vice president of the civic association, told the New York Times that she was not sure how many people were killed, though she knew that the group's secretary and a caseworker were in the building at the time and that English as a second language classes were being held when the shooting started.
"This is the friendliest, nicest place to be," Weisser said. " This is a community where we help with any immigrant issue, with citizenship and translation."
A prayer vigil has been scheduled for Friday evening in Binghamton, a city of about 47,000 located 140 miles northwest of New York City.