NEW YORK -- All 29 people wounded in Saturday's blast in New York City were released from hospitals, Mayor Bill de Blasio said Sunday at a news conference on the explosion.

The mayor called the blast which occurred around 8:30 p.m. Saturday EDT (0030 GMT Sunday)) in the popular Chelsea district in west 23rd street, Manhattan, "a very serious incident", saying lot more work needs to be done to find out the motivation behind the blast.

The motivation behind the explosion remains unknow, Mayor Blasio said.

He termed the blast which wounded 29 people an "intentional" and "criminal" act. However, he declined to call the blast a terrorist attack.

New York City Police Commissioner James O'neil said at the press conference that no one has claimed responsibility for the explosion.

New York police are beefing up extra security at bus terminals, airports and on subways in the city as nearly 200 VIPs and diplomats descended on New York for a Climate Summit and the annual General Debate in the UN General Assembly on Sunday.