THE NEW BILLIONAIRES' ROW: See The Incredible Transformation Of New York's 57th Street

The market for high-end penthouses and ultra-luxury apartments in New York City is booming, and developers are once again building expensive new units after a post-recession slump.

Nowhere is the rise of development more striking than on 57th Street, where six new luxury high rises are under construction, casting long shadows over Central Park and earning the street the nickname "Billionaires' Row."

One57 already stands at 1,005 feet, making it New York's new tallest residential tower. Soon, that title will be surpassed by 432 Park, which will top out at 1,396 feet, and then Nordstrom Tower, which will reportedly rise 1,775 feet in the air when it's completed in several years.

And that's just a sampling of the building spree on 57th Street.

Michael Gross, author of of "House of Outrageous Fortune" and "740 Park: The Story of the World's Richest Apartment Building," told Business Insider that these shiny new skyscrapers are "bizarre throwbacks" and "effectively hotels for foreign money."

"I suspect they will be a 'flash in the pan,'" Gross said. "The motivation to build them doesn't seem to be to build homes for New Yorkers, but to attract investment capital without regard to what sort of homes they will be."

Indeed, many of the new units will be bought as investments, rented out, and flipped for a profit. But whether the glossy highrises of "Billionaires' Row" are a passing fad or mainstay for New York's elite, they are quickly changing the face of the city.