BREAKING: Explosion in US, 29 injured as world leaders arrive for UN General Assembly

At least, 29 people were injured on a crowded sidewalk in the bustling Chelsea neighbourhood of Manhattan, on Saturday night, after a powerful explosion caused by what the authorities said was a homemade bomb, just as world leaders began to arrive for the United Nations General Assembly.

In the Chelsea neighbourhood of Manhattan, which houses the United Nations Headquarters, authorities said detectives later found what they described as a second explosive device four blocks away.

Mayor Bill de Blasio, according to New York Times, called the explosion “an intentional act” but initially said there was no connection to terrorism. But he cautioned that the authorities had just begun their investigation into the blast, which reverberated across a city scarred by terrorism and vigilant about attacks.

“Whatever the cause, New Yorkers will not be intimidated,” he said.

A grim Mr. de Blasio, speaking at a news conference at the scene, said “injuries are significant.” But he said, for the moment, none of them were life-threatening.

Many of the injuries were caused by shrapnel from the explosion, which witnesses said seemed to have come from a sidewalk Dumpster on West 23rd Street near the Avenue of Americas. Images of a twisted Dumpster in the middle of 23rd Street quickly proliferated on Twitter.

The explosion shattered windows, damaged cars and sent crowds running from the scene.

“I heard a big boom,” said Luke McConnell, who was visiting from Colorado and had been headed toward a restaurant on West 27th Street. “I felt it, like a concussive wave, heading towards me.”

“Then there was a cloud of white smoke that came from the left side of 23rd Street near Sixth,” he said. “There was no fire, just smoke.”

Witnesses said they could feel the explosion from several blocks away. Daniel Yount, 34, said he was standing on the roof of a building at 25th Street and Avenue of the Americas with friends.

“We felt the shock waves go through our bodies,” he said.

A law enforcement official said investigators were trying to figure out who was behind the explosion and what the motivations might be.

“It likely came from an improvised device,” said one city official who spoke on the condition of anonymity to discuss an continuing investigation. “We don’t understand the target or the significance of it. It’s by a pile of Dumpsters on a random sidewalk.”

The second device, on West 27th Street, was described as resembling a pressure-cooker like the one used in the Boston Marathon bombings in 2013, the official said.

The official said investigators “don’t have any suspects,” and are not questioning anyone.

The official said that video captured before the explosion shows a man crossing “the street in the direction of where the device was found,” said the official. But there is no video obtained — yet — showing anyone clearly placing the device in the spot where it detonated.

Pressed on who might be responsible for the incident, James P. O’Neill, the police commissioner, said there was no suspect in custody. “We are still in the process of trying to figure that out,” he said.