Ambulances lined the streets of Hoboken, N.J. in the relative calm before Hurricane Sandy last night as Hoboken University Medical Center evacuated patients in the predawn darkness.

Hospitals along the east coast are preparing for the worst, which means postponing elective surgeries, stocking up on supplies, ensuring that backup power generators are ready to go, and, in some cases, evacuating patients.

"Patient safety always is paramount, and although the risks of the hospital losing all power are small, all safety precautions must be taken," said the medical center's CEO, Paul Walker.

Hurricane Sandy is affecting between 50 million and 60 million people as far west as the Great Lakes and as far south as North Carolina, emergency management officials said. They said that Sandy, meeting with a cold front and a high pressure system, could become the worst storm since Hurricane Grace in 1991. Grace was nicknamed the "Perfect Storm. "

The Hoboken hospital evacuated because of fears that surges from Sandy could breach Hoboken's seawall, causing several feet of flooding. The Emergency Room and OB-GYN services for emergency deliveries remained open.

It's taken at lease 40 ambulances from eight counties to complete hospital evacuations in New Jersey, where Sandy is expected to make landfall. Indiana will supply New Jersey with 48 additional ambulances, according to the EMS Task Force Facebook page.

VA New York Harbor Hospital and New York Downtown Hospital were evacuated as well.

Located on the southern tip of Manhattan, New York Downtown Hospital is not far from Battery Park. The hospital itself is not at risk for flooding, but the electrical grid nearby is, said Jeffrey Menke, the hospital's president.

If the hospital loses power, back-up generators can run for 42 hours, but the possibility of not being able to get more fuel after that presented a risk the hospital couldn't take, Menke said.

So on Saturday, all hospital employees were called in to assess their patients for transport. It was "quite an ordeal," Menke said. He said it took 15 hours to move 125 patients to other hospitals.

Through the evacuation, patients, including women in labor, still came for medical help because New York Downtown Hospital is the only one in its area.

"It's not like you just close the doors and you don't take care of patients," Menke said, adding that the emergency department will remain open.

Other hospital systems said they would weather the storm.

North Shore-LIJ Health System's 16 hospitals will remain open, but dozens of critically ill patients whose lives depend on mechanical devices, such as ventilators, were evacuated from Staten Island University Health Center and Southside Hospital, both close to the open water. Both hospitals were completely evacuated during Hurricane Irene last year. For Hurricane Sandy, patients with critical illnesses were evacuated over the weekend and all elective surgeries were canceled.

NYU Langone Medical Center, which also evacuated last year, did not evacuate patients either, but all non-emergency surgeries for Monday and Tuesday have been canceled.

In Delaware, over which Sandy's eye was expected to pass, there have been no hospital evacuations, said Emily Knearl, a spokesman for the state's Health and Social Services Department.