Mayor Bill de Blasio indicated the blast was not accidental, even if there was no known link to terrorism.
"We believe it was intentional. As soon as we're able to determine what specifically caused this explosion, we will report it," de Blasio said.
James O'Neill, who took over as New York police chief only on Saturday after his predecessor resigned, described the Manhattan explosion as "large" and said it happened outside 131 West 23rd Street at 8:30pm.
He added that the building has not been evacuated and that an "extensive search" was being conducted.
The blast occurred in Chelsea -- an area packed with bars, restaurants and luxury apartment blocks -- at a typically bustling time of the weekend.
Police investigated 27th Street for a secondary device as public officials scrambled to reassure the city's 8.4 million residents.
That device -- described by US media as resembling a pressure cooker -- was "safely removed by the NYPD for further analysis" early Sunday, tweeted police spokesman J. Peter Donald.
The explosion came two days before world leaders led by President Barack Obama were due to gather in New York for the UN General Assembly, a time when parts of Manhattan grind to a standstill under draconian security measures.
"There is no evidence at this point of a terror connection to this incident, this is preliminary information," de Blasio told a late-night news conference.
"There is no specific and credible threat against New York City at this point in time, from any terror organization," he added.
AFP reporters saw a massive police presence at the crime scene, where they were joined by FBI and counter-terrorism squads, as police helicopters circled overhead and sirens wailed.
Obama was "apprised" of the explosion and would receive updates on the situati as they become available, a White House official said.
Large boom, then quiet
Of the 29 people who sustained injuries, 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 quiet, then the sound of sirens.
A photograph shared by New York's local NY1 television station showed shattered glass in a doorway, apparently caused by the blast.
Public officials were tight-lipped on the cause of the blast, saying it was still under investigation but confirmed it had not been a gas leak.
New York lauds itself as the safest big city in America. 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.
Trump jumps the gun
Any confirmed attack in New York could impact the country's already deeply divisive presidential election.
Republican nominee Donald Trump jumped the gun on the news reports by saying in Colorado Springs that "a bomb went off in New York."
"We better get very tough, folks, we better get very, very tough," he said.
His Democratic rival Hillary Clinton immediately took swipe at her opponent.
"I think it's always wiser to wait until you have information before making conclusions," she said.
De Blasio said investigators believe there was "no specific connection" to a pipe bomb explosion hours earlier in a trash can in New Jersey.
"It is again too early to say anything definitive on those questions, but there's no specific evidence of a connection at this point," he said.
The New Jersey blast occurred in Seaside Park during a Marine Corps charity run. It caused no injuries but forced officials to cancel the event.
There were up to four timed explosives but only one detonated, Al Della Fave, a spokesman for the Ocean County prosecutor, told CNN.
The mayor said that the police department and all other agencies -- including the city's "anti-terror capacity in particular" -- were 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 terror plots since September 11, 2001 when nearly 3,000 people were killed.
New York Governor Andrew Cuomo said state officials were coordinating with federal and city authorities.
"We are closely monitoring the situation and urge New Yorkers to, as always, remain calm and vigilant," Cuomo said in a statement.
source: interaksyon.com
