NEW YORK (AP) -- A spokesman says the United Nations is assessing security in the wake of an explosion in New York's Chelsea district as the organization prepares to host world leaders arriving for the General Assembly.
"There is no specific and credible threat to New York City from any terror organization," de Blasio said at a news conference late Saturday night.
However early indications were that the attack was intentional, de Blasio said.
"We believe at this point in time this was an intentional act. I want to assure all New Yorkers that the NYPD and ... agencies are at full alert," he said.
There was no sign that the explosion was caused by a natural gas explosion, New York Police Commissioner James O'Neill said at the press conference.
Based on what is currently known, there was also no connection to the incident earlier Saturday in Seaside Heights, N.J., where a pipe bomb exploded near a Marine charity run, de Blasio said. In that instance the device was placed in a garbage can. No injuries were reported.
Manhattan Borough President Gale Brewer said the Chelsea explosion was not in a dumpster but next to one in the street.
NYPD spokesman Peter Donald said authorities were also investigating whether a second device had been found near site of earlier explosion. Police asked residents to avoid the area around 27th Street between Sixth and Seventh avenues.
Blast at 8:30 pm
The explosion came just after 8:30 p.m. ET at 133 W. 23rd St., between Sixth and Seventh Avenues. None of the injuries appeared to be life-threatening, the New York City Fire Department said.
The cause of the explosion has not been determined. "The investigation is active and at this time an extensive search is being conducted,” New York Police Commissioner James O'Neill said at the press conference.
"The area around the explosion site is being treated as a crime scene," O'Neill said.
Several injured were transported to area hospitals, assistant commissioner for communication with the New York City Police Department J. Peter Donald tweeted.
The explosion area occurred a block away from Eataly, a popular Italian market and eatery. The neighborhood has many late-night and after-hours music clubs. At 11 p.m., New York police and news helicopters hovered over the scene beneath a full harvest moon.
The New York Police Counter-Terrorism unit responded to the blast and transit service in the area was shut down, according to the New York Fire Department.