NYC Mayor DeBlasio: Chelsea explosion 'intentional', but no immediate terror link

An explosion shook the Chelsea section of New York City on Saturday, injuring dozens after a blast of unknown origin detonated near a heavily-trafficked commercial and residential area.

Around 8:30 p.m. Eastern, an explosion rattled buildings in the area of West 23rd Street, one of NYC's more bustling areas teeming with nightlife. The blast sent pedestrians scrambling for cover and injured nearly 30 people, officials said.

NYC's mayor's office told NBC News early Sunday that an object police described as a "possible secondary device" was found nearby on West 27th Street and had been removed.

The device was taken aboard a special containment vessel to the NYPD's range at Rodman's Neck in the Bronx. Law enforcement sources described the find as a pressure cooker with items attached, according to NBC News.

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At a press conference, NYC Mayor Bill DeBlasio stated there was no immediate indication of a terror connection, and downplayed the suggestion that the explosion might be connected to an earlier incident in New Jersey. However, DeBlasio added the blast appeared to be deliberate, with authorities saying the blast was not connected to a gas explosion.

"We believe it was intentional, and a full investigation is underway," DeBlasio told reporters. Despite bearing the hallmarks of terrorism, officials appeared to carefully calibrate their public remarks to allow for the possibility that the blast could be arson or vandalism.

According to New York City officials, at least 29 people were being treated for various minor injuries, with at least one considered serious. On Sunday morning, the NYC Health + Hospitals/Bellevue said that all of the 11 patients it had received had been treated and released.

A senior city official told WNBC-New York that officials were investigating whether something may have been planted in a garbage can or dumpster.

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A witness near the scene told CNBC that the blast was enough to shake buildings in the immediate vicinity, and that police were instructing residents to remain indoors and clear the scene.

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A White House official said that President Barack Obama was briefed on the news, and would be kept abreast of developments.

The incident came on the heels of a device of unknown origin that exploded in Seaside Park, on the New Jersey shore, earlier in the day. No casualties or injuries were reported, but local police said a pipe bomb had exploded near the route of a charity race, and the incident is being investigated as an act of terror.

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Coming as it did in the wake of that event, a number of social media users expressed incredulity that the Chelsea blast was not immediately labeled terrorism.

--WNBC-New York, CNBC's Katie Little and Natalie Barnard contributed to this article.