An explosion in a crowded Manhattan neighbourhood has left 29 people injured, and authorities say a second nearby site is also being investigated.
New York Mayor Bill de Blasio called the blast on Saturday an "intentional act", but said there was no terrorist connection.
"Tonight, New York City experienced a very bad incident," de Blasio said at a news conference near the scene in Chelsea.
"We have no credible and specific threat at this moment."
De Blasio said the blast was "an intentional act" and tried to calm any fears among nervous New Yorkers, saying the explosion had no terrorist connection and wasn't related to a pipe bomb explosion earlier on Saturday in New Jersey at a charity run.
A law enforcement official told The Associated Press that a second device that officers were investigating four blocks from the scene appeared to be a pressure cooker attached to wiring and a mobile phone.
The source, speaking on condition of anonymity because the person was not authorised to speak about an ongoing investigation, said the device was found inside a plastic bag on West 27th St.
A law enforcement official told The Associated Press that the explosion appears to have come from a construction toolbox in front of a building. The official spoke on condition of anonymity.
New York officials said the incident was not due to a gas leak.
The blast happened on West 23rd street, in front of a residence for the blind, near a major thoroughfare with many restaurants and a Trader Joe's supermarket. Witnesses say the explosion at about 8:30pm blew out the windows of businesses and scattered debris in the area. Officials said no evacuations were necessary.
Police spokesman J Peter Donald said several people were taken to hospitals with injuries. One of the injured suffered a puncture wound that was considered serious. Officials said the other injuries were minor, described as scrapes and bruises.
Donald tweeted a warning to residents near the second site that officials are investigating, saying: "As a precautionary measure, we are asking residents who live on West 27th St between 6th and 7th Avenues in Manhattan to stay away from windows facing 27th St until we clear the suspicious."
A number of New York City subway routes were affected by the earlier explosion.
The White House said President Barack Obama has been apprised of the explosion in New York City and will be updated as additional information becomes available.
In St Cloud, Minnesota, police said multiple people were injured at a shopping mall Saturday evening in an attack that possibly involved both a shooting and stabbing. The suspect was believed to be dead.
The reports of a possible blast come hours after a pipe bomb exploded in Seaside Park, New Jersey, shortly before thousands of runners participated in a charity 5K race to benefit Marines and sailors. No injuries were reported.