With New York Governor Andrew Cuomo alongside, New York Mayor Bill de Blasio, seen shaking hands with a policeman, surveys the site of an explosion which occurred in the Chelsea neighborhood of New York, US, September 18, 2016. [Photo/Agencies]

New York police are beefing up extra security at bus terminals, airports and on subways in the city for the UN General Assembly week.

In an earlier press briefing, New York State Governer Andrew Cuomo also said the state will be deploying an additional 1,000 state troopers and members of the National Guard throughout New York City.

The suspects and motives were still unknown, and investigations were still in early stages, according to city officials.

Also on Saturday night, a man wearing a private security company uniform stabbed nine people at a mall in St. Cloud, 65 miles (105 km) northwest of Minneapolis, the capital of the US state of Minnesota, before an off-duty police officer shot him dead.

Three of the nine victims were hospitalized, one with life-threatening injures, local police said on Sunday at a news conference.

The Islamic radical group ISIS has claimed responsibility for the mall stabbing attack, CNN reported on Sunday.

The US Federal Bureau Investigation has investigated the Minnesota stabbings as a "potential" act of terrorism.

CNN cited a police chief in St. Cloud as saying that there was no evidence at this point of a link between the New York blast and the mall stabbing spree.