Mayor Bloomberg said Monday that New York City remains a top terrorism target and that "the killing of bin Laden will not change that."
"Nor will it distract us from a mission that remains our absolutely highest priority: defending our city and country against all those who use violence to attack freedom," Bloomberg said at a ground zero news conference.
New Yorkers are seeing extra police at airports, bridges, tunnels and the World Trade Center site itself following Osama bin Laden's death.
There was also an obvious increased police presence on subways Monday, and Police Commissioner Ray Kelly said there would be much more that civilians would not see.
Kelly said the NYPD's "assumption is that bin Laden's disciples would like nothing better than to avenge his death with an attack in New York."
He said security at landmarks and other forms of transportation, like ferries, is being ramped up. MTA Chairman Jay Walder said riders would also see extra bag searches and heavy weapons teams on trains and buses.
Heavily armed Amtrak police accompanied by K-9 units met commuters Monday at Penn Station.
Video: Crowds Chant After Bin Laden Death
The NYPD says the stepped-up security is a precaution. The mayor and police commissioner stressed Monday that there's no immediate information indicating a specific threat to New York City.
Some New Yorkers expressed relief for the additional security and said city police should continue to provide it, regardless of bin Laden's death. Others didn't feel any imminent threats connected to the terrorist's demise.
"I don't think levels of danger really change just because one person died, so I don't think it's that different," said commuter Jason Lydon, of Union City, N.J., at Penn Station.
Judy Banez, a nurse who commutes to New York City from Pennsylvania and lived in Queens on 9/11, said she was happy bin Laden was killed and had no problem with the added security.
"We're being vigilant and we can now go on with our lives," she said.
The Port Authority of New York and New Jersey "out of an abundance of caution" said it is also adding more police at the facilities it runs, which include the airports, the George Washington Bridge and ground zero.
The measures aren't in response to any specific threat and all the facilities will operate normally otherwise, the Port Authority said.
Eighty-four Port Authority employees died in the attack on the World Trade Center on Sept. 11, 2001.
In a phone interview with NBC's Matt Lauer Monday morning, former Mayor Rudy Giuliani said he felt it was "very appropriate" that both the city and country be on heightened alert in the wake of bin Laden's death.
"I think in the short run this could be dangerous for us," Giuliani said. "In the long run, this is a very very good development in the war against Islamic extremist terrorism. He was a major symbol and you cannot underestimate the value of taking out a major symbol like that, but in the short run, this could create problems for us that we have to be very alert to."
There have been a number of foiled plots targeting New York City since the terrorist attacks on Sept. 11, 2001.
There was the 2009 arrest of Najibullah Zazi, who later confessed to plotting an attack on the subway system. And it was just one year ago Sunday when Pakistani-American Faisal Shahzad tried to ignite a car bomb in Times Square.
In response to those investigations, police have expanded programs to monitor the sale of homemade bomb ingredients and have expanded the use of license plate readers, cameras and radiation detectors.
New Yorkers have grown accustomed to enhanced security in the city, and while they recognize the need for it, many refuse to allow the potential threat associated with bin Laden's death or the inherent threat of living in a big city that's been attacked before to inhibit their daily lives.
Jay Snyder, who commuted from Huntington, on Long Island, Monday, said an attack might happen at any time.
"You never know so I think you just gotta keep living like we should 'cause ... we can't let them win that way."