Authorities believe the bomb was placed intentionally but is not terror related, and New York governor Andrew Cuomo said there was no evidence of an "international terrorism connection" and there was no connection with or claim of responsibility from so-called Islamic State, although the investigation was at a "very, very early stage".
A secondary device was identified near to where the explosion took place in the Chelsea area of the city but was removed safely by New York Police's bomb squad.
The New York City mayor Bill de Blasio said: "There is no evidence at this point of a terror connection. There is no specific and credible threat against New York City at this point in time from any terror organization."
The explosion occurred at around 8.30pm on Saturday evening (12.30am UK time) in the popular neighbourhood between Midtown and Lower Manhattan.
"The NYPD Bomb Squad and the FBI Joint Terrorism Task Force were requested to respond," said New York Police Commissioner James O'Neill.
"As of this time, the exact cause of this explosion has not been determined. Investigation into this incident is active at this time and an extensive search is being conducted. The area around the explosion site is being treated as a crime scene."
Cuomo said there was no immediate threat to the city but an additional 1,000 police officers and National Guard will be deployed across the ciuty, including at airports, bus terminals and subway stations.