Mayor Bill de Blasio said Saturday that an explosion that rocked Manhattan's Chelsea neighborhood Saturday night is not thought to be an act of terror, hours before bomb squad members safely removed a second suspicious device found four blocks away from the blast.

The NYPD announced at around 2:30 a.m. Sunday that authorities had safely removed what appeared to be a pressure cooker attached to wiring and a cellphone, which was discovered inside a plastic bag on West 27th Street between Sixth and Seventh avenues.

It was unclear whether the materials comprised an explosive device or whether it was just someone's trash.

The discovery was made not long after an explosion on West 23rd Street, possibly in a dumpster, sent shock waves down the block between Sixth and Seventh avenues at around 8:30 p.m., injuring more than a dozen people.

In a press briefing shortly after 11 p.m. the mayor said the blast was not thought to be an act of terror -- but that authorities have deemed it "an intentional act."

NYPD Commissioner James O'Neill, in his first full day on the job following the departure Friday of long-time NYPD head Bill Bratton, said that the exact cause of the explosion has not been determined, but that the area around the site is being treated as a crime scene.

FDNY Commissioner Daniel Nigro said that 29 people were injured in the blast, most of them suffering minor injuries with one serious.

"Tonight New York City experienced a very serious incident," de Blasio said. However, he said that "there is no evidence at this point of a terror connection."

Several businesses on 23rd Street shut down in the aftermath of the explosion, and authorities there cordoned off several buildings, eventually allowing residents back in several hours later.

ConEd crews were on the scene, as were officials with the FBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

Preliminary reports point to the explosion happening inside of a dumpster or construction toolbox, but authorities would not confirm either possibility during their briefing.

Witnesses reported feeling the ground shake, and photos posted online showed broken glass in nearby buildings. Other witnesses say patrons were ushered out of nearby restaurants for their own safety after the blast occurred.

Authorities shut down 23rd Street between Fifth and Eighth avenues in the aftermath of the explosion.

Following the incident, the MTA stopped 1 and 2 train service between Penn Station and Chambers Street in both directions, but service was restored shortly before 11 p.m. M5, M7 and M23 buses were also detoured around the area.

Stay with NY1.com for more information on this developing story.