A law enforcement source said an initial investigation suggested the explosion occurred in a dumpster but the cause was still undetermined. CNN reported that law enforcement sources believe an improvised explosive device caused the blast.

At least three people were seen being taken away from the scene of the blast in ambulances, but the severity of their injuries was not immediately clear. A car seen driving through the area had its rear window blown out. The blast occurred at about 8:30 p.m. (0030 GMT Sunday) between 6th Avenue and 7th Avenue on 23rd Street, a major east-west thoroughfare in the fashionable downtown neighborhood of Chelsea, J. Peter Donald, a deputy commissioner with the New York Police Department, said in a Twitter message.

Representatives of the NYPD, the Fire Department of New York and other city agencies could not be reached immediately for further comment. Twenty-five civilians were confirmed to have been injured in the blast, the New York City Fire Department said on Twitter.

The explosion, described by one neighbor as "deafening," happened outside the Associated Blind Housing facility at 135 W. 23rd Street. The facility provides housing, training and other services for the blind. Hundreds of people were seen fleeing down the block on a cool early autumn evening, as police cordoned off the area. "It was really loud, it hurt my eardrums. My 10-year-old boy was sat in the back seat of the car, and the explosion blew the back window out," said Tsi Tsi Mallett, who was in a car driving along 23rd Street when the explosion took place. Her son was not injured.

Neha Jain, 24, who lives in the neighborhood, said she was sitting in her room watching a movie when she suddenly 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. Then we could smell smoke. Went downstairs to see what happened and firemen immediately told us to go back."

New York City Police issued a bulletin advising motorists in the area that they should "expect extensive traffic delays and emergency personnel in the area of 23rd Street and 7th Avenue" due to police activity there and asking the public to avoid the area.

Earlier Saturday, a pipe bomb exploded in a plastic trash in along the route of a charity road race in the New Jersey beach town of Seaside Park, but no injuries were reported in what authorities believe was a deliberate attack.

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