When superstorm Sandy hit NYU Langone Medical Center Monday night, cutting off the power to the New York City hospital, doctors and nurses rose to the occasion.

In one of the most heart-stopping events of the storm, the staff began an unprecedented emergency evacuation of hundreds of patients, including 20 newborns, from the hospital in downtown Manhattan.

Everything had gone dark. Respirators and machines failed. The elevators froze shut.

"It was a pretty dramatic situation, and the staff at NYU is amazing, what they were able to do," Dr. Ira Parness, chief of Mount Sinai's Division of Pediatric Cardiology, said. "No elevators, they were able to transfer sick babies, take them down flights of stairs to waiting ambulances and move them all safely. They really did an amazing job getting the patients out safely."

The evacuation came after a power outage caused by Sandy, followed by a failure of backup generators at the hospital because of flooding in the basement. Having survived Hurricane Irene last year, the hospital did not anticipate the surge from New York's East River would do such damage.

The first move was to assign a nurse and doctors to every patient until they made it down the stairs, according to the hospital. One of them was Maraget Chu, who gave birth to baby boy Cole close to midnight on Monday just before the storm began to pound the hospital.

"On the 13th floor you can really hear the winds howling, and it was really strong," Chu recalled

Just six hours after her son's birth, Chu and her husband, Greg Prata, learned they would have to evacuate. Guided by a nurse who was wielding a flashlight and carrying their precious cargo, Cole and his parents made their way down the stairwell.

The family shared the steps with other patients, who were being carried out on plastic sleds, rushed by firefighters and paramedics.

"All of these firemen who were carrying these women who were gurneyed to these sleds," Chu said. "It was pretty amazing. You saw them just dipping with sweat and just carrying these women who couldn't walk down the stairs."

Nurses and paramedics carried 20 babies down from the neonatal intensive care unit on the ninth floor, wrapping them in blankets for the journey down a dark and chaotic stairwell.

Prata said they were "lucky" compared with some women who had even less time between giving birth and the evacuation.

"We were lucky when we were going down that stairwell," Prata said. "Patients, most of them, were women who had just delivered and were having some issues, and so they had to stop and regroup. At which point we just slid right by them."

Twenty-four ambulances lined the street, waiting to be waved in to pick up patients from NYU Langone. The patients were moved to a number of area hospitals, according to officials at NYU.

Chu, Prata and Cole were rushed to nearby Lenox Hill Hospital, which took in 86 patients from NYU Langone as a result of the storm.

"He came in a little bit damp … but no worse for the wear," a nurse on Cole's medical team at Lenox Hill told ABC News.

Hurricane Sandy: Full Coverage

"It was our pleasure," Lenox Hill Hospital's Dr. Arthur Klein, SVP for Children's Services, North Shore-LIJ Health System, told ABC News' David Muir. "It's why we're in this profession."

As this was unfolding, new mom Shel-lasha Wimms, 17, was home on New York's Long Island, thinking of her baby girl. O-Rianna was born premature with a heart condition Oct. 13, and had been kept at the hospital for monitoring for a few weeks.

Wimms called to make sure everything was OK as the hurricane approached but turned on the news and said she saw the evacuation under way.

"I was trying to look closely to see if it was her," Wimms said.

She raced in from storm-ravaged Long Island to Manhattan find her baby girl. When Wimms arrived, she was told her baby had been taken to Mount Sinai Hospital, nine blocks away. Heroic nurses had shuttled her baby to safety.

"I'm very thankful for them, because without them it's not a possibility that my daughter could have been here right now," Wimms said.

It took a total of 12 hours to evacuate the building, but all patients reportedly arrived at other hospitals safely.

"It's really a very dramatic event and a testimony to their level-headedness and professionalism," Dr. Ira Parness, chief of Mount Sinai's Division of Pediatric Cardiology, said of the NYU staff. "I think this is just one in many happy ending stories for this really devastating hurricane."