Mayor Bill de Blasio called Saturday’s bombing in Chelsea intentional, but he said there was “a lot more work” to be done before authorities will be able to establish a motive for the explosion, which wounded 29 people.

“We know there was a bombing, that much we do know,” he said at a news conference on Sunday afternoon, urging New Yorkers to be vigilant and to call police with any information.

Later Sunday, investigators were reviewing surveillance video that shows a person of interest around the device that detonated.

Sources familiar with the investigation said Sunday that police will be using facial recognition software and other technology to help assess the image on the video.

“What this guy’s role is is not crystal clear,” one of the sources said.

Additional surveillance video shows the moments before, during and after the explosion, with people running down the street fleeing from debris.

De Blasio said that New York will see an NYPD presence this week that’s “bigger than ever.” The city initially boosted its police presence for the U.N. General Assembly this week, and Gov. Andrew Cuomo has now deployed an additional 1,000 uniformed officers, including National Guard members, to airports, subway stations and other high-profile locations.

NYPD Chief of Department Carlos Gomez said New Yorkers will see more cops, counterterrorism teams, heavy weapons units, bag checks and K9 units during their commutes.

Cuomo said earlier on Sunday that the bombing was "obviously an act of terrorism," but that there was no apparent link to terror groups overseas.

When asked about de Blasio’s Saturday remark that there was no link to terrorism, Cuomo said that the mayor meant there was no evidence of an overseas terror connection. He added, “Now it depends on your definition of terrorism. A bomb exploding in New York is obviously an act of terrorism, but it's not linked to international terrorism.”

Police Commissioner James O'Neill said at a news conference Sunday that authorities are "not discounting anything at this point." If authorities determine a motivation, O'Neill said that they'd "say it loud and clear."

“If it is an act of terrorism, we’re going to come out and say it,” he said.

Cuomo pledged to find the person or people responsible for the bombing and said that "they will be brought to justice, period.”

“We will not allow these type of people and these type of threats to disrupt our life in New York," he said. "That’s what they want to do, we're not gonna let them do it. This is freedom, this is democracy and we’re not going to allow them to take that from us.”

Authorities said that the 29 people wounded in the explosion on West 23rd Street between Sixth and Seventh avenues have since been released from the hospital. One person suffered a puncture wound, and others had scrapes and abrasions from glass and metal, the FDNY said.

Cuomo said that there has been “significant property damage on both sides of the explosion,” but FDNY Commissioner Daniel Nigro said that there was no structural damage to the affected buildings. Cuomo also said there was no damage to the nearby subway and PATH stations.

Authorities responded to the blast at 131 W. 23rd St. just after 8:30 p.m. when police officers from the 10th Precinct witnessed the explosion and called for backup, O'Neill said at a news conference Saturday.

State police who were patrolling the area then found a second device on West 27th Street between Sixth and Seventh avenues. Law enforcement sources said it was a pressure cooker with a cellphone and wires attached to it. The NYPD said the bomb squad safely removed the device by around 2:20 a.m. on Sunday, and that it's being worked on in the Bronx by the bomb squad.

A third suspicious package, at Fifth Avenue and West 28th Street, was determined to be garbage, police said.

Cuomo said that the FBI had taken evidence from the explosion site, as well as "the bomb that did not detonate" and would review it at the agency's lab in Quantico. The FBI was also reviewing materials found in Seaside Park, New Jersey, where a pipe bomb exploded earlier Saturday along the route of a race for Marines.

Cuomo said he had spoken with New Jersey Gov. Chris Christie and that the two were coordinating resources to "see if there's anything we can learn." 

Sources close to the investigation said the Chelsea bomb is being studied for any link to the Seaside Park bomb, based on the similarity of the detonators used and that the explosives were not complex.

The NYPD closed some streets surrounding the crime scene and the MTA had several subway lines bypassing 23rd and 28th streets, but normal service has since resumed.

Cuomo and de Blasio toured the site together on Sunday and then visited several nearby storefronts, where they took photos with people and assured them that the situation was under control.

President Barack Obama, who was attending a congressional dinner in Washington, "has been apprised of the explosion in New York City, the cause of which remains under investigation," a White House official said. "The president will be updated as additional information becomes available," the official added.

The explosion quickly became an issue in the presidential race, with Republican candidate Donald Trump remarking about the blast when he appeared at a Colorado rally.

"Just before I got off the plane, a bomb went off in New York, and nobody knows exactly what's going on," Trump said hours before New York officials spoke publicly about the explosion. "We better get very tough, folks."

On Sunday, Trump tweeted his "best wishes" to those who were impacted by the blast.

"I would like to express my warmest regards, best wishes and condolences to all of the families and victims of the horrible bombing in NYC," he tweeted

Meanwhile, in a statement on Sunday, Democratic rival Hillary Clinton condemned the New York and New Jersey bombings, as well as the Minnesota mall stabbings, referring to the three incidents as "apparent terrorist attacks." The Islamic State's news agency has claimed that the suspect in the Minnesota mall attack was a "soldier of the Islamic State," but no one has claimed responsibility for either bombing.

"Law enforcement officials are working to identify who was behind the attacks in New York and New Jersey and we should give them the support they need to finish the job and bring those responsible to justice - we will not rest until that happens," Clinton said in the statement.

Witnesses and nearby residents described the "deafening" Chelsea explosion and the aftermath of the blast.

"It was really loud, it hurt my eardrums. My 10-year-old boy was 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."

Nita Patel, 36, lives on 23rd Street, right next to where the explosion occurred. 

Patel was in TriBeCa at 8:30 Saturday night when her neighbor called. 

"My neighbor called and said, 'Did you feel the shake?'" she recalled. "We drove up and parked the car in the garage and then cops said, 'You're not going back up.'"

Patel and her family, including two young kids, had to camp out at a friend's house on 22nd Street. By Sunday morning, they couldn't get back inside to pick up any essentials. Both children clutched stuffed animals. 

"It's a total crime scene," she said. "I don't know what's going to happen with school."

Zach Schute, 27, is the facilities manager at Peloton Cycle, a cycling gym on 23rd Street. Evidence markers and debris littered the street in front of the storefront. 

"I tried to come last night but everything was blocked off," he said. "Our whole front is just glass. I want to check if it's broken."

Schute said he will wait on the corner of Seventh Avenue "as long as I have to. There's not much I can do." 

- With Newsday and Reuters