NYC Mayor Bill de Blasio speaks during a press conference...

NYC Mayor Bill de Blasio speaks during a press conference on Fifth Avenue and East 79th Street to discuss the Orlando mass shooting, Sunday, June 12, 2016. Credit: Jeff Bachner

This story was reported by Anthony M. DeStefano, Alison Fox, David M. Schwartz and Rachel Uda.

New York City went on high alert, and authorities in Nassau and Suffolk counties increased counterterrorism patrols Sunday morning, just hours after 50 people were killed in a shooting in Orlando, Florida, in what became the worst mass shooting in the nation’s history.

Federal officials were investigating the shooting as an act of terrorism.

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New York City went on high alert, and authorities in Nassau and Suffolk counties increased counterterrorism patrols Sunday morning, just hours after 50 people were killed in a shooting in Orlando, Florida, in what became the worst mass shooting in the nation’s history.

Federal officials were investigating the shooting as an act of terrorism.

“We have put all the police forces on the state side, state of New York, on high alert,” said Gov. Andrew M. Cuomo, who was marching in the New York Puerto Rican Day Parade. “There will be extra deployment at places of mass gatherings, such as this parade, transportation centers, etc., which is our normal protocol when there has been a possible terrorist attack. . . . We’re increasing the police presence in critical areas across the state.”

New York City Mayor Bill de Blasio, also marching in the parade, was quick to reassure residents that extra security was in place.

“We have close coordination with all of our federal partners, with the Joint Terrorism Task Force, the FBI and all our partners,” the mayor said. “We are vigilant.”

Stephen Davis, the NYPD’s deputy commissioner for public information, said the department placed its patrol and counterterrorism resources — including the Critical Response Command, Strategic Response Group and Emergency Services Unit — “on alert pending further information.”

NYPD Chief of Department James O’Neill said that over the next few days, New Yorkers can expect to “see increased uniform presence in nightlife throughout the city, in crowded venues.

“We will be working with the LGBT community, not just in Manhattan, in the outer boroughs also, to make sure that we deploy properly to make people not only safe, but to feel safe throughout the city. And that’s what we do so well.”

The NYPD’s counterterrorism chief, James Waters, said the department — for now — will defer to the Orlando investigation. “Right now we are going to let the Orlando police and the FBI down in Florida conduct the investigation,” he said. “As it warrants, they will send us leads if they need us to check out anything.”

The NYPD said it has more than 500 officers “dedicated solely to terror response, hundreds more to the prevention of incidents, and is constantly working with law enforcement and community partners to counter terror.”

Nassau County Executive Edward Mangano and acting Police Commissioner Thomas Krumpter said the Nassau County Police Department is intensifying patrols around all areas of public gatherings and critical infrastructure.

A Suffolk police department spokeswoman said the department is monitoring the Orlando shooting investigation and was in contact with law enforcement partners, including the FBI.

“We will adjust our posture accordingly as information develops,” she said in a statement.

Suffolk police had an increased presence at an LGBT event Sunday afternoon in Sayville “as a precautionary measure and to make people feel at ease,” Commissioner Timothy Sini said.

De Blasio said all flags should be flown at half-staff and the city will light City Hall in rainbow colors to represent LGBT pride at sunset.

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