The Department of Homeland Security also provided intelligence to federal air marshals for domestic and international flights and to customs and border officials. A bulletin summarizing the incident was also sent to the nation's 18,000 law enforcement agencies.
The Connecticut license plate on the car does not match the vehicle, and investigators have spoken to the individual to whom the plates are registered, according to Kelly.
That license plate ultimately was traced to a Connecticut junkyard, officials said.
The car bomb was discovered when a T-shirt vendor saw something suspicious -- smoke coming from an unoccupied SUV on 45th Street near 7th Avenue -- so he alerted police.
The tip led to what New York Mayor Michael Bloomberg called an "amateurish"-looking car bomb that Secretary of Homeland Security Janet Napolitano told ABC News' "This Week" might have been part of a "one-off" attack.
The 6:30 p.m. scare prompted police to evacuate thousands of people from the heart of the Big Apple during one of its busiest times -- a warm Saturday night when it was packed with theatergoers and tourists.
"We are very lucky," Bloomberg said. "Thanks to alert New Yorkers and professional police officers, we avoided what could [have been] a very deadly event."
Authorities were examining security cameras and other evidence to see if they could identify a possible suspect or motive -- and already had located video of the car being driven to the scene.
"Right now, we have no evidence that this was anything but a one-off" attack, Napolitano told "This Week" this morning.
"Tape is being reviewed and additional forensics are being done in addition to that," she added. "Times Square, I think, now is safe."
President Obama was being kept informed on the investigation by Deputy National Security Advisor John Brennan, who was communicating with the New York Police Department and other investigators, the White House announced Saturday evening.
"This is a bomb. This is a car bomb -- a crude device that includes gasoline, propane and is wired together," Browne said Saturday night.
"The wiring ... looked amateurish, I think, is a nice way to phrase it," Bloomberg added early today. "It was made up of consumer-grade fireworks that you can buy in Pennsylvania and drive into New York.
"It certainly could have exploded and had a pretty big fire, and a decent amount of explosive impact," Bloomberg said.
Richard Clarke, a former counterterrorism czar under Presidents Clinton and Bush, told ABC News' "Good Morning America" that he expects to see an arrest in the case.
"You can be pretty certain this guy will be found," he said, "because of all the videotapes, because the bomb not [fully] going off left a wealth of evidence."
He suggested the incident shows how an alert populace can help foil an attack.
"It's a reminder to all of us, whether we're in airports or train stations, subways, if we do see something that looks a little suspicious, it's much better to call it in than to have the guilt afterwards that you didn't," Clarke said.
The T-shirt vendor, who's a Vietnam veteran, noticed smoke coming from the vehicle at around 6:30 p.m. Saturday and notified a mounted police officer.