A powerful blast injured 29 people in the Chelsea neighbourhood of Manhattan and a second suspicious device was found blocks away, New York police said Sunday.
Mayor Bill de Blasio told reporters the explosion, which took place late Saturday outside a building on West 23rd Street, was an "intentional act" but said there was no evidence yet of a terrorism connection.
The blast blew out nearby windows and hurled debris across the street, images posted on social media and surveillance video showed.
According to the New York City fire department, 29 people were injured, of whom 24 people were hospitalized.
A second suspicious device was discovered at short time later on West 27th Street. A bomb disposal unit removed it from the area for analysis, police said.
The device was described as a pressure cooker with wires coming out of it, US media reported citing law enforcement sources.
The White House said President Barack Obama was receiving updates on the investigation.
The New York City incident comes after a bomb hidden in a garbage container exploded Saturday in the state of New Jersey along the planned route of a charity run sponsored by the US Marines, causing no injuries.
De Blasio said there were currently no indications of a connection to the earlier blast in New Jersey.