Multiple people were hurt after an explosion in New York City on Saturday, September 17, that Mayor Bill de Blasio is calling "an intentional act."

The explosion occurred at about 8:30 p.m. in the Chelsea neighborhood of Manhattan, on West 23rd Street between Sixth and Seventh Avenues, in front of a residence for the blind.

The New York Police Department tweeted that 29 people were injured, with one considered serious. None of the injuries are believed to be life-threatening.

"There is no evidence at this point of a terror connection to this incident," de Blasio told reporters at a press conference, adding that "the initial indication is this was an intentional act."

The NYPD later tweeted that a "possible secondary device" was found by investigators a few blocks away shortly after 11 p.m. and residents were warned to stay away from windows facing 27th Street until the area was cleared.

A law-enforcement official told the Associated Press that the second device, which was found inside a plastic bag, appeared to be a pressure cooker attached to wiring and a cellphone.

CNN reports that police are reviewing video from the scene that likely shows someone dropping or leaving something behind, and that the explosion was in a Dumpster or some kind of receptacle.

NYPD Police Commissioner James O'Neill said in a statement that an extensive search is being conducted and "the area around the explosion site is being treated as a crime scene."

"There was a loud boom and our entire apartment shook," Neha Jain, 24, who lives on West 23rd and Sixth Avenue, told NBC News. "All the pictures fell to the floor and then I heard people screaming."

De Blasio said that the investigation has found no link to an explosive device that blew up in Seaside Heights, New Jersey, earlier on Saturday, along the planned route of a 5k Marines charity race.

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