NEW YORK, USA — A bomb that exploded in New York wounding 29 people and causing significant damage was under investigation yesterday as an act of terror, although officials say there is no overseas link.

The blast tore through Chelsea — one of the most fashionable districts of Manhattan packed with bars, restaurants and luxury apartment buildings — late Saturday at around 8:30 pm local time.

Police later discovered a second bomb four blocks away, which was safely defused and taken away for analysis.

The attack put New York on full alert, just one day before world leaders are due to gather in the city for the United Nations General Assembly.

It came as a jihadist-linked news agency claimed that an Islamic State group “soldier” carried out a stabbing attack in a shopping mall in Minnesota that left eight people injured also late Saturday.

Local police said the attack “made some references to Allah”, but the motivation of the attack was unclear. The attacker was shot dead by an off-duty police officer.

In New York, police and law enforcement have sealed off the traffic for five blocks around the scene and dozens of officers were out in force Sunday.

An AFP photographer said there were lots of debris, including rubble and glass, on 23rd Street where the explosion happened.

“Whoever placed these bombs, we will find and they will be brought to justice,” New York Governor Andrew Cuomo told reporters at the scene.

“A bomb exploding in New York is obviously an act of terrorism, but it’s not linked to international terrorism. In other words, we find no ISIS connection, et cetera,” said Cuomo in reference to the Islamic State extremist group based in Iraq and Syria.

“But a bomb going off is generically a terrorist activity. That’s how we’ll consider it. And that’s how we will prosecute it,” he added.

An extra 1,000 state police and National Guard will deploy to airports, bus terminals and subway stations to reassure New Yorkers returning to work on Monday that the city is up and running, he said.

“We have no reason to believe at this time that there is any further immediate threat,” Cuomo said.

He said that while there was no evidence of an international terror link “at this time”, it was still “very early in the investigation”.

The explosion outside a building on 23rd Street, between Sixth and Seventh Avenues, caused “significant” property damage with glass and shrapnel “everywhere”, the governor said.

While the two devices planted in Manhattan appear to be similar, at this stage they seem to be different than a pipe bomb that exploded in the neighbouring state of New Jersey on Saturday, he said.

The New Jersey blast occurred in Seaside Park during a Marine Corps charity run and caused no injuries.

There were up to four timed explosives, but only one detonated, Al Della Fave, a spokesman for the Ocean County prosecutor, told

CNN.

Of the 29 people who sustained injuries in New York, 24 were taken to hospital with various degrees of scrapes and abrasions from glass and metal, said Fire Department Commissioner Daniel Nigro.

Witnesses living three blocks away told AFP they heard a large boom from their fifth-floor apartment, followed by the sound of sirens.

New York lauds itself as the safest big city in the United States. Violent crime has become rare in Manhattan and stringent security checks the norm in many areas since the 2001 Al-Qaeda hijackings destroyed the Twin Towers.

The explosion in New York, the country’s largest city, its financial and entertainment capital as well as home to the two presidential candidates, could impact America’s divisive presidential election.

“I would like to express my warmest regards, best wishes and condolences to all of the families and victims of the horrible bombing in NYC,” Republican nominee Donald Trump tweeted Sunday.

On Saturday, way before officials confirmed the cause of the explosion, Trump said it had been a bomb.

His Democratic rival Hillary Clinton immediately took swipe at her opponent, although later also used the word “bombings” to refer to what had happened in New York and New Jersey.

New York Mayor Bill De Blasio said that police, law enforcement and the city’s “anti-terror capacity in particular” was on full alert.

The city routinely goes on extra security alert following attacks in other American cities or in Europe, and police claim to have foiled multiple alleged terror plots since September 11, 2001 when nearly 3,000 people were killed.