The episode began when a person in a passing vehicle tossed a cylindrical object into the police van late yesterday, said Chief of Department James O'Neill.
The officers sped to a less crowded neighborhood and notified the bomb squad.
"These two officers are heroes of the NYPD, heroes of New York City," Police Commissioner William Bratton tweeted.
"I look around, saw a lot of kids, a lot of young people," Armani said at a news briefing. "We both look at each other and I go, 'We're going to go, but I'm not going to have anyone else go with us."
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His partner, Officer Peter Cybulski, said he was "nervous" as Armani drove to a less crowded spot.
The object turned out to include a candle and a harmless electrical component. A police photo showed them displayed beside foil and white cloth.
The suspect "rolls up the window, puts his hands towards the glove compartment and says that he wants to die and has a bomb strapped to his vest," said Bill Aubry, chief of Manhattan detectives.
Aubry said the man put on a red helmet and continued to act erratically.
SWAT officers closed in.
Surrounding streets were closed and subway trains bypassed the area, a traffic circle at the southwest corner of Central Park that is home to the Time Warner Center and the Trump International Hotel and Tower.