An explosion rocked Manhattan on Saturday night in what is, "according to early indications, an intentional act," as New York Mayor Bill de Blasio announced Saturday evening. An apparent second device was then found, unexploded, just four blocks away.

The mayor and James O'Neill—in his first full day on the job as New York City Police Commissioner—stressed that there was no evidence so far to link the explosion to terrorism and no known specific threat against the city. However, New York Gov. Andrew Cuomo said Sunday morning that the explosion was “obviously” terrorism, but cautioned that it was not linked to international terrorism.

Even though there is no additional known threat to New York City, Cuomo ordered additional police patrols in airports and subway stations as a precaution.

De Blasio said there is no indication the explosion is connected to an earlier incident in which a pipe bomb went off at a charity run in New Jersey.

The Daily Beast's Tim Teeman, who was on the scene, reported hearing a bang and smelling something burning. "I've never heard a bang like it," he said.

The explosion occured at 23rd St. and 6th Ave., a largely commercial intersection, shortly after 8:30 p.m. Twenty-nine people were treated for injuries, some "significant" but none life-threatening so far, de Blasio said. All 11 of the victims who were taken to Bellevue Hospital were released by 8:30 a.m. on Sunday morning, a spokeswoman confirmed.

A graphic cellphone video of the immediate aftermath of the explosion, aired by local news station NY1, showed a bleeding, shocked woman walking to an ambulance.

The NYPD opened a second crime scene on 27th St. between 6th and 7th Avenues, where police found a pressure cooker with wires coming out of it, described as similar to the devices used in the Boston Marathon bombing. The device was removed in the early hours Sunday morning by the NYPD bomb squad.

The NYPD asked residents there to stay away from windows facing 27th St. as officers cleared the scene, and 7th Avenue was entirely cleared of pedestrians and automobile traffic.

There were some reassuringly New York City sights as the wait continued at the police line set up at the corner of 27th St. and Seventh Avenue: A kid on a bike tried to whizz past the barricade. When told that he couldn't, he zoomed handsomely in the opposite direction.

Donald Trump took the opportunity to blame terrorists just 45 minutes after the explosion, and before almost any facts had emerged.

"I must tell you that 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 really in a time—we better get tough folks," Trump said upon landing in Colorado.

Hillary Clinton said aboard her campaign plane that she was briefed about the explosion and "I'll have more to say about it when we actually know the facts."

Mayor de Blasio and Commissioner O'Neill said there is no reason to believe that the Chelsea blast was linked to the explosion in a garbage can of part of a three-pipe bomb device before a Marine Corps marathon on the Jersey Shore Saturday morning. The race was then cancelled.

"Whatever the cause," of the Chelsea blast, said de Blasio, "New Yorkers will not be intimidated."

— with additional reporting by Tim Teeman and Andrew Desiderio.