At least 29 people were injured in an explosion in Chelsea neighbourhood of Manhattan in New York, authorities said, hours before world leaders arrive here for the high-level UN General Assembly session.
President Barack Obama has been apprised of the explosion, a White House official said.
New York City Mayor Bill de Blasio said the city "experienced a very serious incident" and injuries are significant but added that there is "no evidence at this point of a terror connection" even as early indications suggest "this was an intentional act".
"There is no specific and credible threat at this time from any terror organisation", he said.
Blasio said the number of people injured is now 29 but none is life threatening except for one who is in "serious" condition.
A second Manhattan site is under investigation, Blasio said while addressing a press conference at the scene.
The explosion - which came hours after a pipe bomb went off in a garbage can in New Jersey - occurred in Manhattan's Chelsea neighbourhood at 23rd St. and 6th Avenue, a busy residential and commercial area frequented by tourists and city residents, around 8:30 pm (local time) yesterday.
The New York Police Department said a "possible secondary device" has been located at 27th Street, 6th-7th Avenues.
Citing local and federal law enforcement officials, CNN reported that the device found at the second spot appears to be a pressure cooker with wires hanging out.
Police said investigations are ongoing and advised people to avoid the area.
As a "precautionary measure" residents living in the 27th street between 6th and 7th avenues to "stay away" from windows facing 27th street "until we clear the area of a suspicious package", they said, adding this is a precautionary measure only and they are not evacuating the area.
The Mayor also added that at this point there is "no specific connection" to the incident in New Jersey earlier in the day in which an explosion occurred in a garbage can.
"We are not going to let anyone change us, intimidate us," the mayor said.
Authorities said "extensive search" is being conducted in the area and the neighbourhood and ruled out gas as the reason for the explosion.
Security is already tight in the city as nearly 190 world leaders, including Obama, will arrive in the city for the about week-long high-level annual UN General Assembly session, beginning tomorrow.
FBI and Homeland Security officials were at the scene, a local official told the US media.
The New York Times quoted an official as saying that "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 investigators "don't have any suspects", and are not questioning anyone.
The explosion in one of the most fashionable districts of Manhattan comes a week after America's financial capital with an 8.4 million population marked the 15th anniversary of the 9/11 attacks.
It which occurred at usually a busy time of the weekend in an area packed with bars, restaurants and luxury apartment blocks.
"The president (Obama) has been apprised of the explosion in New York City, the cause of which remains under investigation. The president will be updated as additional information becomes available," a White House official said.
Obama is scheduled to travel to New York and stay in the city for the next several days to attend the United Nations General Assembly session.
Of those injured, 24 have been taken to hospitals with scrapes and abrasions from glass and metal, Fire Department commissioner Daniel Nigro said.
Police said they have video from the scene and are collecting more, according to CNN. However, police said it is too early to give out details beyond saying the explosion was outside, in a dumpster or receptacle of some kind. They are processing the scene.
Police are combing through the video and that it likely shows someone dropping or leaving something behind, leading them to the conclusion this was an intentional act.
An eyewitness was quoted as saying that he was having dinner when an explosion rocked the area.
"(I) felt a loud explosion and I felt like a lightning bolt struck the building. It, like, shook the ground," he said. "Everybody ran out of the restaurant into the street. The whole city was in the street.”
Democratic presidential nominee Hillary Clinton was also briefed about the New York explosion. She was in the Washington DC addressing the Congressional Black Caucus dinner.
The 68-year-old former secretary of state cautioned against drawing conclusions on the New York explosion before facts are in.
Asked what she thought of her Republican opponent Donald Trump immediately referring to the explosion as a bomb earlier, Clinton said: "I think it's important to know the facts about any incident like this."
Referring to the explosion, Republican presidential nominee Donald Trump had said "a bomb went off" in New York "just before I got off the plane."
"We better get very tough. We'll find out. It's a terrible thing that's going on in our world and in our country and we are going to get tough and smart and vigilant. We'll see what it is," Trump told supporters at an election rally in North Carolina.
(With PTI inputs)
