New York ( CNN ) -- They called them the `` human bucket brigade . '' National Guard troops lined up in stairwells at Bellevue Hospital , carrying oil for generators up 13 flights of stairs . Superstorm Sandy had knocked out the hospital 's power , and flooding had wiped out basement fuel pumps designed to power its generators . On Wednesday , when officials at one of the country 's largest hospitals decided the storm damage was too extensive to keep the facility running , those same troops helped carry patients down flights of stairs to waiting ambulances , said Alan Aviles , president of New York City Health and Hospitals Corporation . The troops were `` tireless , '' he said , thanking them for their efforts . Dr. Gupta : Saving Baby Emma in the storm . More than half of the 725 patients who were inside Bellevue when the storm hit have been transferred , Aviles told CNN on Wednesday evening . The remaining 260 patients will be evacuated by Thursday , he said . Dozens of ambulances lined up outside the hospital to carry patients to other facilities . Officials had hoped to keep the hospital running , Aviles said , but an investigation Wednesday revealed that the damage had been too extensive . `` The emergency generators were just not enough to keep this hospital operating for the long term , '' he said . Bellevue is along the East River , just north of Manhattan 's 26th Street . Floodwaters poured into the massive hospital 's 1-million-square-foot basement , Aviles said , damaging fuel pumps and water pumps that supply the complex . None of the hospital 's 32 elevators is working , he said . `` It was obviously not anticipated that we would get a storm surge of this magnitude . ... We 've never seen anything like this at Bellevue Hospital , '' Aviles said . Officials estimate that 17 million gallons of water rushed into the hospital 's basement , he said . 7 ways to manage stress in a disaster . Most of the critically ill patients have already been evacuated , said Dr. Sanjay Gupta , CNN 's chief medical correspondent , who was reporting from outside the hospital Wednesday . Gupta said moving such patients is a particularly difficult process . `` It can be very challenging ... even to transfer them within the hospital from one floor to the next . That can be a real challenge , '' Gupta said . `` It 's a very coordinated process . You always plan for the worst-case scenario . Everything from a patient 's heart rate to their body temperature can change . '' Gupta said evacuating the remaining patients is `` likely to be more methodical , a little bit slower , perhaps even look a little more organized than over the last 24 hours . '' Aviles told reporters that it was too soon to tell when the hospital would be up and running again . `` If we can get this hospital back and operating in two or three weeks , we will be doing very well , '' he said . Hurricane safety : When the lights go out . Bellevue is just a few blocks away from NYU 's Langone Medical Center , where staff evacuated about 260 patients -- including newborn babies that had been in intensive care -- after the storm hit . At times with only flashlights to illuminate the way , hospital employees carried some patients down 15 flights of stairs to ambulances ready to take them to the safety of other hospitals . Langone did n't anticipate such heavy flooding from Sandy and chose not to evacuate all its patients before the storm . But as the storm hit Monday night , the hospital 's basement , lower floors and elevator shafts filled with 10 to 12 feet of water , and the hospital lost its power , according to Dr. Andrew Brotman , senior vice president and vice dean for clinical affairs and strategy . `` Things went downhill very , very rapidly and very unexpectedly , '' Brotman said . `` The flooding was just unprecedented . '' NYU doctor to CNN 's Piers Morgan : `` We are always prepared '' CNN 's Elizabeth Cohen and Matt Sloane contributed to this report .
NEW : ` ` We ' ve never seen anything like this , '' a hospital administrator says . National Guard troops carried patients out of the hospital , he says . After the storm , troops used a ` ` fire truck '' to carry fuel to generators . The hospital is near another hospital used to evacuate patients after the storm .