New York City Mayor Bill de Blasio and other city officials said investigators had ruled out a gas leak as the cause of the blast.
New York City Mayor Bill de Blasio and other city officials said investigators had ruled out a gas leak as the cause of the blast, but they stopped short of calling it a bombing and declined to specify precisely what they believed may have triggered the explosion.
Neha Jain, 24, who lives in the neighborhood, said she was sitting at home watching a movie when she heard a huge boom and everything shook.
"Pictures on my wall fell, the window curtain came flying as if there was a big gush of wind," she told Reuters.
"Then we could smell smoke. We went downstairs to see what happened, and firemen immediately told us to go back."
Police said a sweep of the neighborhood following the blast had turned up a possible "secondary device" four blocks away consisting of a pressure cooker with wires attached to it and connected to a cell phone.
CNN, citing law enforcement sources, reported that a piece of paper with writing on it was found nearby.
Residents living nearby were advised to stay away from windows facing the street as a precaution, and the item was later safely moved to a police firing range for further examination, officer Christopher Pisano said.
Pressure cookers packed with explosives and detonated with timing devices were used by two Massachusetts brothers in the 2013 Boston Marathon bombing that killed three people and wounded more than 260.
The latest blast came less than a week after law enforcement agencies around the country were on heightened alert for the 15th anniversary of the Sept. 11, 2001, airline-hijacking attacks that killed nearly 3,000 Americans in New York, Washington and Pennsylvania.
Remaining circumspect about the exact nature of the explosion in Chelsea, De Blasio said early indications were that it was "an intentional act." He added that the site of the blast, outside on a major thoroughfare in the fashionable lower West Side Manhattan neighborhood, was being treated as a crime scene.
"There is no evidence at this point of a terror connection," the mayor said at a news conference about three hours after the blast.
"There is no specific and credible threat against New York City at this point in time from any terror organization."
The mayor also said investigators did not believe there was any link to a pipe bomb that exploded earlier on Saturday in the New Jersey beach town of Seaside Park. No injuries were reported in that blast, from a device planted in a plastic trash can along the route of a charity foot race.
But a U.S. official said that a Joint Terrorism Task Force, an interagency group of federal, state and local officials, was called to investigate the Chelsea blast, suggesting authorities have not ruled out the possibility of a terror connection.
A joint task force also took the lead in investigating the New Jersey incident.