A woman jumped 20 stories to her death from a swanky rooftop bar in the Flatiron District Monday night.

As onlookers sipped pricey drinks at the 230 Fifth Rooftop Bar during a corporate party at 7:30 p.m., 30-year-old Faigy Mayer suddenly sprinted toward a row of bushes that lined the edge of the establishment, cops and onlookers said.

She went through the shrubbery, over a wall and plummeted to the sidewalk on West 27th Street, shocking pedestrians.

“I was waking across the street and I saw she was falling,” said Dale Martin, who witnessed the tragedy. “You can tell it was a lady. She had on shoes and a dress.”

The section of the bar where Mayer jumped was cordoned off by police as they investigated.

“There was a big corporate party up there and she kind of ran through them [the partygoers] and jumped,” said another witness Becky Whittemore.

“They closed off the section where she jumped from. I think a lot of the people up there had zero clue what was going on.”

Officials recovered two bags that might have belonged to the victim, a purse and a backpack.

It was not known if Mayer was connected to the party.

After the tragedy, some bar patrons still enjoyed table service at the establishment, where bottles can fetch as much as $300 each.

Although police sources said the woman likely jumped deliberately, one patron said that the bar’s tiny four-foot-wide ledge was barely enough to keep boozed-up partygoers from accidentally toppling to their doom.

Carlos Rodriguez, 51, of Gramercy said he was inebriated one night and perched himself on the edge for a picture.

“I sat at the ledge of the roof and was drunk out of my mind,” Rodriguez said.

“I was able to sit there and nobody gave a sh-t.

“They really need to be more careful up there. There’s nothing to keep you from jumping,” he added.

The bar bills itself as “New York’s largest outdoor rooftop garden and fully enclosed penthouse lounge.”

One floor is fully enclosed and “our rooftop garden is open to the sky,” its Web site says.

Additional reporting by Larry Celona and Joe Tacopino