An explosion in New York City's Chelsea neighborhood Saturday night that injured at least 29 people appears to have been "an intentional act," Mayor Bill de Blasio said, and a possible second device was removed several blocks away.

The mayor said that although investigators believe it was intentional, there appeared to be no link to terrorism.

The cause of explosion has not been determined, said New York City police commissioner James O'Neill.

There is no credible threat to the safety of New Yorkers, the officials added.

Bomb-sniffing dogs deployed in NYC's Chelsea neighborhood after reported explosion. Follow @ABC for latest. pic.twitter.com/fH6uF0hGqD

— Paul Blake (@PaulNBlake) September 18, 2016

The "large explosion" on 23rd Street between Sixth and Seventh Avenues was seen by police officers driving by around 8:30 p.m., according to police. The fire department heard the explosion and responded immediately.

ABC

Of the 29 injuries, one is considered to be serious, police said.

Officials said the NYPD has video it is reviewing and De Blasio urged any witnesses or people who may have information to come forward.

Two law enforcement sources said the explosion occurred in a dumpster, and the NYPD Counterterrorism Bureau tweeted a photo of a mangled dumpster, after tweeting that they were responding to the explosion.

The New York Police Department Bomb Squad was searching the area, checking garbage cans, for any other possible explosive devices.

Surveillance video recovered from West 23rd Street shows the explosion and contains other evidence that indicates to investigators that the original object was intentionally left next to the construction trash container, described as 4 ft. by 4 ft. by 3 ft. in size. In one video obtained by police, a man is seen crossing the street in the vicinity of where the original object was left. The trash container was blown clear into the street by the force of the blast. 

The object left behind could be a large tool box, left next to one of the several commercial trash containers in front of a building that has been under construction. Investigators are trying to determine if there is a connection to this seemingly "random construction site." 

The explosion even startled residents who were a few blocks away. Chelsea resident Michelle Leifer was walking her dog in Madison Square Park when she heard a loud boom and rumbling. "I heard a loud boom and felt rumbling," she tells ABC News. "I wasn't sure if it was an explosion or if a large truck had gone by. One of the park's maintenance men came in and said he got an alert on his phone that there was an explosion on 23rd and 6th. As I was leaving the park, I saw a smoke cloud hovering in that area. Then police cars and firetrucks started streaming in."

The Associated Press

Meanwhile, a "possible secondary device" was located a few blocks away on 27th Street, between 6th Avenue and 7th Avenue, the NYPD Special Operations Division said around 11 p.m. The device, a pressure cooker, was removed by authorities. The device was in a white plastic bag with tape, wiring and a cell phone or other electronic device.

There were other suspicious packages and incidents in the area since the pressure cooker was discovered, but the packages and incidents were deemed not dangerous.

The explosion occurred one day after O'Neill was sworn as the new police commissioner following Bill Bratton's retirement.

The mayor said the Chelsea explosion has no apparent connection to the explosive device that detonated in Seaside Park, New Jersey, Saturday morning. Nobody was injured in the New Jersey incident, which occurred at a time when a 5k run to benefit U.S. Marines and sailors was scheduled, but the race was delayed because so many runners had signed up.

This is a developing story. Check back for more.