New York Mayor Bill de Blasio said a second site was being investigated.
"Tonight, New York City experienced a very bad incident," de Blasio said at a news conference near the scene. "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 Saturday in New Jersey at a charity run.
A law enforcement official said the explosion appears to have originated from a construction toolbox in front of a building. The official spoke on condition of anonymity because the person wasn’t authorised to speak about an ongoing investigation, AP reports.
The blast happened on West 23rd street, in front of a residence for the blind, near a major thoroughfare with many restaurants. Witnesses say the explosion at about 8:30 p.m. 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 and was considered serious. Officials said the other injuries were minor, described as scrapes and bruises.
The FBI and Homeland Security officials, along with the ATF arson and explosive task force are also at the scene. 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.
A second device was found four blocks away on West 27th Street. According to several local news sources, it was a pressure cooker attached to a mobile phone by tape with protruding wires.
People living on West 27TH Street were instructed to stay away from their windows while the device was investigated. Police, aided by sniffer dogs, combed refuse bins to ensure there were no other devices.
Reacting to the blast, Republican Presidential candidate Donald Trump said: "It is a terrible thing what's going on in our world, what's going on in our country, but we are going to get tough and smart and vigilant and we are going to end it."
The explosion come hours after a pipe bomb went off in Seaside Park, New Jersey, shortly before thousands of runners participated in a charity 5K race to benefit Marines and sailors. The device, which only partially detonated caused no injuries. Authorities are yet to make any connection between the explosion.
Hillary Clinton says she has been briefed about the bombings in New York and New Jersey and the attack in Minnesota.
She says the nation needs to support its first responders and "pray for the victims".
"We have to let this investigation unfold," she said.
In St. Cloud, Minnesota, police said multiple people were injured at a shopping mallSaturday evening in an attack that possibly involved both a shooting and stabbing. The suspect was believed to be dead.