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An explosion that injured 29 people when it rocked a crowded Manhattan neighborhood Saturday night has been determined to be an "intentional act," and New York Gov. Andrew Cuomo said it was clearly "an act of terrorism."

The explosion, on West 23rd Street between Sixth and Seventh avenues in the Chelsea neighborhood, was reported around 8:30 p.m. Twenty-nine people were hospitalized with injuries, but they had all been released by Sunday afternoon, authorities said.

"A bomb exploding in New York is obviously an act of terrorism," Cuomo said Sunday morning.

Latest developments:

Surveillance video may show the same man at both locations where devices were found

New suspicious package discovered in New Jersey

"Vehicle of interest" stopped in New York late Sunday

Governor orders 1,000 state troopers and National Guard soldiers to New York City

Authorities investigating 911 call claiming responsibility

Both NYC "bomb" and explosive device in New Jersey used flip-phones

Less than three hours after the blast, an object police described as a "possible secondary device" was found just a few blocks away from the original explosion on 27th Street while officers were combing the area. Cuomo said the device was "similar in design" to the one that detonated just blocks away.

Authorities studying surveillance video on Sunday from both areas may have identified the same man at each location, law enforcement sources told NBC New York.

.@BilldeBlasio and @NYGovCuomo review damage from last night’s explosion in Chelsea. Mayor to NYers: “Be vigilant." pic.twitter.com/eZEHzj4h9r — NYC Mayor's Office (@NYCMayorsOffice) September 18, 2016

The device from the second location was later sent to an NYPD range in the Bronx aboard a special containment vessel, New York Mayor Bill de Blasio's office said. The device was "rendered safe" and was being sent to a special FBI facility in Quantico, Va., for examination, police said Sunday night.

Meanwhile, the FBI confirmed that a "vehicle of interest in the investigation" was stopped near the Verrazano Bridge in New York late Sunday. No one had been charged, and "the investigation is ongoing," said a spokesperson who gave no further details.

And police and the FBI responded late Sunday night to a suspicious package near the Elizabeth transit station at 11 West Street. Authorities didn't say whether they believed the package might be related. New Jersey Transit suspended service between Newark Airport and the Elizabeth station.

De Blasio said Saturday night that the blast hadn't been linked to terrorism, but Cuomo clarified that the explosion hadn't been linked to an international terrorist group. "A bomb going off is generically a terrorist activity," Cuomo said.

PHOTOS: New York Emergency Crews Respond to Blast Scene

De Blasio and other city officials stressed that the investigation was in its early stages and that while investigators had been able to determine that the blast was "criminal" and "intentional," they hadn't nailed down a suspect or a motive.

No arrests have been made, but NYPD Commissioner James O'Neill said, "New York City residents can rest assured that we'll get to the bottom of this."

Still, O'Neill, who was sworn in just a day before the blast, said the situation worried him. "We did have a bomb detonated on 23rd Street, and we have no one apprehended, so of course I'm concerned."

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Security had already been tightened in the city for the ongoing United Nations General Assembly, but the presence of officers throughout New York City after the blast will be "bigger than ever," De Blasio said.

Cuomo ordered 1,000 New York State police and National Guard members across the city.

Police had said the blast in the Chelsea neighborhood appeared to come from inside a large trash bin, and law enforcement sources said they have video of a man dropping something into or next to a dumpster on 23rd Street.

Another video from 27th Street shows a man leaving behind a piece of luggage before two other people come along, take a device out of the bag and walk away with just the suitcase, officials familiar with the investigation said.

Again, we urge and remind everyone, if you have any information on the Chelsea explosion share it by calling #800577TIPS — NYPD NEWS (@NYPDnews) September 18, 2016

Videos like that — from nearby businesses — are what detectives want to get their hands on from both 23rd and 27th streets to see who was there before the explosions, New York Police Chief Carlos Gomez said.

He said the investigation would take time. "There's a lot of people out on the street on a warm Saturday evening in Manhattan," he said.

A 911 call, in which the person on the line claimed responsibility, is also being looked at, but officials don't know whether the call was legitimate or a hoax.

New Yorkers were encouraged to remain vigilant Sunday and to call police with any information they may have about either device.

The explosion sent a dumpster flying more than 150 feet down the sidewalk and shattered windows more than a block away, a senior law enforcement official said.

After viewing the extensive destruction, Cuomo said it was "fortunate" that no one had been killed. "When you see the damage, it's amazing that no one was killed, to tell you the truth. We're lucky that only 29 were injured," Cuomo said Sunday on MSNBC.

President Barack Obama was apprised of the situation, a White House official said.

"The initial indication is this was an intentional act," de Blasio told reporters at the Saturday night news conference.

There was also "no specific and credible threat against New York City at this point in time from any terror organization," the mayor added.

Cuomo reiterated Sunday morning that there was no further credible threat, and he urged New Yorkers to "err on the side of caution" but feel comfortable to go about their daily business.

"We will not allow these type of people and these type of threats to disrupt our life in New York. That's what they want to do, and we're not going to let them do it," Cuomo said.

"They want to make you worry about going into New York City or New York state. We're not going to let them instill fear, because then they would win," he added.

"Bottom line on this is ... whoever placed these bombs we will find, and they will be brought to justice," Cuomo said. "Period."

'Entire apartment shook'

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

Jain said the explosion shattered the glass in her building's lobby. "My first thought was it's a bomb," Jain said. "It's quite terrifying."

A large police presence, including officers of the New York Office of Emergency Management and the NYPD's counterterrorism unit, responded to the scene.

There is a construction site near the scene of the Chelsea explosion. Police searched cars and trash cans in the area.

Facebook activated its "Safety Check" feature so that users can easily notify friends and family members of their status.

De Blasio also said the investigation has so far found no link to an explosive device that blew up in a New Jersey Shore community earlier Saturday, near a planned race route.

But officials familiar with the investigation said flip phones were found in the pipe bomb in New Jersey and the pressure cookers in New York, leading investigators to wonder whether the two incidents are connected. They stressed that it's still too early to tell.

In that incident in Seaside Park, a device of three pipe bombs exploded along the planned route of a Marines 5K charity race. No one was hurt. The device was placed in a trash can in that incident, NBC New York reported.

Democratic presidential candidate Hillary Clinton said Saturday night that she was briefed about the explosion, as well as the explosive device in New Jersey, but she said she wouldn't have more to say on the New York incident until more is known.

"Obviously, we need to do everything we can to support our first responders. Also to pray for the victims," she said.

Mentioning a third attack by a man with a knife in St. Cloud, Minn., Clinton said in a statement released Sunday: "I strongly condemn the apparent terrorist attacks in Minnesota, New Jersey, and New York. I pray for all of those who were wounded, and for their families."

Nine people were hurt in the knife attack at a Minnesota mall hours before the blast in New York. An ISIS-affiliated news outlet claimed that the attacker was "a soldier of the Islamic State," according to NBC News terrorism analyst Flashpoint Intelligence, a global security firm.

"Americans have faced threats before, and our resilience in the face of them only makes us stronger. I am confident we will once again choose resolve over fear," Clinton said in response to the three incidents.

Huge explosion in Chelsea blew this dumpster ... pic.twitter.com/1lSIGjRyC8 — Chris Duffy (@voicehalf) September 18, 2016

Her Republican rival, Donald Trump, mentioned the explosion at the start of an event in Colorado Springs on Saturday, saying a "bomb" went off in New York. His remarks came before authorities had said the explosion was the result of a bomb.

"Just before I got off the plane, a bomb went off in New York, and nobody knows exactly what's going on, but boy, we are living in a time," Trump said. "We better get very tough, folks."