Ruslana Korshunova, 20, whose face has graced the cover of French Elle and Russian Vogue, apparently jumped from her ninth-floor apartment in her Water Street building in the Financial District just before 2:30 p.m.
"I heard what sounded like a gunshot or a bomb or an explosion," said a stunned Con Ed worker talking to a cop nearby before the beauty leaped.
"I looked down the street, and I say to the cop, 'Did that person just get hit by a car?' " said the worker, who identified himself only as Patrick, 32, of Brooklyn.
The two men raced over. "Her arms were crushed," Patrick said. "Her head was on the left side and blood was coming out in a pool."
Cops said there were no signs of a struggle in the apartment.
The window from which she fell had a balcony, which had construction netting around it that appeared to have been cut.
The 5-foot-8 head-turner has been featured in ads for DKNY, Vera Wang and Christian Dior among others and was hailed as "the next big thing" in a profile in Vogue three years ago.
"She's one of the sweetest, nicest people you'll ever meet," said a friend, who did not want to be identified by name.
"I'm still in shock. The world lost a great person."
The lithe looker has been a mainstay at Fashion Week in the Big Apple and London, working with all-star designers Jill Stuart, Betsey Johnson, Rosa Cha, Lela Rose and Libertine.
The pal said that Korshunova had just returned from a modeling gig in Paris and seemed to be "on top of the world."
"There were no signs," he said. "That's what's driving me crazy. I don't see one reason why she would do that."
Korshunova, who had been sending money back to her parents in Kazakhstan, was in love with the city.
"She really liked New York," said the friend. "People made her feel comfortable here."
Korshunova's doorman, who did not want to be identified, remembered the catwalker as "very soft-spoken."
"She always said hi and bye," he said. "She was beautiful, beautiful."