evacuated, New York Mayor Michael Bloomberg said on Wednesday.
About 500 patients at the city hospital near the East River in Manhattan are affected. Bellvue has one of the busiest emergency departments in the city.
Several area hospitals, including The Mount Sinai Hospital and St. Luke's Roosevelt Hospital Center, have agreed to take some of Bellevue's patients.
``We learned this morning that Bellevue will now have to evacuate because of damage that it has sustained,'' Bloomberg told a news conference.
``They didn't think the damage was that bad, and they had a generator going. But the bottom line is when they got into the basement they realized there was more damage,'' Bloomberg said.
Outside Bellevue , the oldest of New York's public hospitals, a long line of ambulances waited to ferry patients to other medical centers.
A handful of New York hospitals had already been evacuated due to the storm that caused record flooding in parts of the city.
New York University's Langone Medical Center near the East River was forced to evacuate all 215 of its patients, including critically ill infants, when its backup generator failed after some eight feet of water flooded its basement.
The Manhattan Veterans Affairs Hospital and the New York Downtown Hospital, both in low-lying areas of lower Manhattan, evacuated patients before the storm hit, and Brooklyn's Coney Island Hospital near the Atlantic Ocean beaches was later evacuated.
A spokeswoman for New York Presbyterian Hospital said it was accepting transfers from Bellevue, but she was unsure of the number. It had already taken patients from three other medical centers, including NYU Langone.
Bellevue, known for its psychiatric care facilities, has many other therapeutic departments. The hospital has long been an important resource for the city's poor and uninsured.
Jarron Franklyn, 28, who works in Bellevue's rehabilitation department, said: ``The power is down, and we have flooding in the basement.'' He said a back-up generator was still running.
A New York Police Department spokesman said National Guard members were assisting with the Bellevue evacuation.
Dennis Jiosne, 34, a patient from Point Pleasant, New Jersey, was evacuated by stairs from the hospital's 16th floor. He said National Guardsmen in the stair well were passing people food and water.
Jiosne, who was being treated for a septic ulcer, said the power went out two days ago and there was no running water in his room. He appeared to be taking it in stride.
``In my unit it really wasn't bad, aside from the plumbing and the food,'' he said. ``I'm a pretty resilient guy. I was content in my room. The lack of television was an inconvenience.''