An “intentional” blast has injured at least 29 people in the Chelsea district of New York City, officials say.

The cause of the blast on September 17 remains unclear.

NYC Mayor Bill de Blasio described the explosion as “intentional” but said that there were no known links to terror.

The force of the explosion blew-out windows and could be heard several blocks away.

Officials later told media that a device was found at a second location in the same district.

None of the injuries is life-threatening but one is serious, New York’s fire commissioner said.

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Most of those hurt suffered cuts and other minor injuries from glass and other debris.

The blast occurred around 21:00. Witnesses said people ran in all directions following the “incredibly loud” blast.

Unconfirmed reports said the explosion went off in a dustbin. Several blocks have been closed down by police.

Bill de Blasio said: “We do not see a link to terrorism.”

The mayor said it was too early to determine the cause but added: “We believe it was intentional.”

Bill de Blasio also said there was no evidence of a link to a pipe bomb explosion in neighboring New Jersey hours earlier.

According to law enforcement officials, the device found at the second Chelsea location appeared to be a pressure cooker attached to wiring and a mobile phone. Police said it had been removed safely.

Chelsea is among the most fashionable districts of Manhattan and its bars and restaurants are usually crowded at the weekend.

President Barack Obama is being kept up to date on the investigation, a White House official said.

Hillary Clinton told reporters she had been in touch with New York officials.

“Obviously we need to do everything we can to support our first responders and pray for the victims,” the Democratic presidential nominee said.

“I’ll have more to say about it when we actually know the facts,” she added.

Speaking at a rally in Colorado before police had commented on the cause of the blast, Republican presidential candidate Donald Trump told supporters that a “bomb” had gone off.

He said: “Nobody knows exactly what’s going on, but boy, we are living in a time – we better get very tough, folks.”

The earlier bomb explosion in Seaside Park, New Jersey, on September 17 came shortly before thousands of runners were to participate in a charity race there. No injuries were reported.

On September 20, President Barack Obama and other world leaders are due to attend the UN General Assembly in New York.