An explosion near a dumpster on West 23rd Street at Sixth Avenue injured 29 people, sources said. View Full Caption Twitter/@NYPDCT

MANHATTAN — Twenty-nine people were injured in an explosion on West 23rd Street Saturday night that Mayor Bill de Blasio called an "intentional act."

The blast occurred near a rolling Dumpster at 131 W. 23rd St. at Sixth Avenue around 8:30 p.m., the NYPD and sources said.

The mayor called the explosion a "very serious act" but said there was "no evidence at this point of a terror connection." Gov. Andrew Cuomo on Sunday morning said that while there was no link to "international terrorism," it was not yet clear whether there was a domestic terror link.

A suspicious package was also being investigated nearby on West 27th Street between Sixth and Seventh avenues, police said. Residents were asked to stay away from their windows as a police robot investigated that device.

That package contained a pressure cooker with a cellphone taped to it that looked like an explosive device, but it wasn't clear whether it was actually a bomb, sources said.

►READ MORE: Here's What We Know — And Don't Know — About the 23rd Street Explosion

Most of those injured on West 23rd Street were taken to area hospitals. One of them was believed to have serious injuries. The others had bruises and cuts from glass and metal, FDNY Commissioner Daniel Nigro said. None of those injuries are considered life-threatening.

Eleven of the victims were taken to Bellevue Hospital, treated and released, according to the hospital's Twitter account.

We received a total of 11 patients from the 23rd St. explosion that occurred on Sept. 17. All patients have since been treated & released. — BellevueHospital (@BellevueHosp) September 18, 2016

Three of the injured refused treatment at the scene, an FDNY spokesman said Sunday. The rest of the victims were released from area hospitals by Sunday morning, Cuomo said.

Nigro also said that so far a connection has not been found between an earlier incident in New Jersey when a pipe bomb exploded near a military race, and that it was too early to tell whether the explosion was linked to the United Nations General Assembly which opened Thursday.

Police Commissioner James O'Neill, who was on his first day on the job as police commissioner after Bill Bratton officially retired Friday, said that police officers were driving westbound on West 23rd Street when they witnessed the explosion, but the exact cause of it was still unknown.

Investigators have ruled out a gas or other utility issue as a cause, sources and officials said.

The blast was stronger than an explosion from a homemade device left in Central Park that seriously wounded a college student over the Fourth of July weekend, sources said.

The NYPD Counterterrorism Unit responded to the explosion as well as the FBI's Joint Counterterrorism Task Force, and de Blasio said the NYPD is on "full alert." Cuomo on Sunday said he deployed 1,000 State Police and National Guardsmen to the city in an "abundance of caution."

Sixth avenue remains closed off to traffic between 14th and 27th streets, according to the NYPD. In addition, 23rd Street between Fifth Avenue and Seventh Avenue has been closed, while 24th through 27th streets have been closed between Broadway and Seventh Avenue, police said.

Helicopters and sirens could be heard in the neighborhood, according to witnesses, but people in the area appeared calm.

Helicopters swarming over my apartment with a spotlight. #chelseaexplosion — Alysse (@xo_Alysse) September 18, 2016

I'm in Chelsea and nobody in New York is panicking. Nor should you, wherever you are. #ChelseaExplosion — Seth Porges (@sethporges) September 18, 2016

The investigation caused subway service disruptions on several subway lines. 1 and 2 trains were suspended between Chambers Street and 34th Street for several hours but resumed service while continuing to skip 23rd Street, according to the MTA.

#ServiceAlert: b/d there is no 1 & 2 train service b/t Chambers St & 34 St, due to NYPD activity at 23 St. See https://t.co/vhZQ2kZ2vb — NYCT Subway (@NYCTSubway) September 18, 2016

F train service resumed but continued to skip 23rd Street Saturday overnight, the MTA said.

E trains were skipping 23rd Street.

Full service was expected to resume on the subways by Monday morning, Cuomo said.

Check the MTA's website for updates on service.

De Blasio asked New Yorkers to stay vigilant and keep calm after the explosion.

"Whatever the cause, whatever the intention here New Yorkers will not be intimidated," he said. "We will not let anyone change who we are and how we go about our lives."

The NYPD asked anyone with information about the explosion to call the Crime Stoppers Hotline at 1-800-577-TIPS, or for Spanish, 1-888-57-PISTA (74782).

— Additional reporting by Paul DeBenedetto.