Police were stationed throughout Bellevue, and were limiting visitors' access to the main lobby entrance unless they were there to see family members.
On Monday night, patients were evacuated from New York University Langone Medical Center. A stream of ambulances evacuated patients from the hospital after backup generators failed following a power outage, city officials said.
NYU Langone Medical Center spokesman Christopher Rucas told ABC News Tuesday that more than 300 patients had been safely moved out of the hospital and transferred to surrounding institutions. Dozens of these were critical care patients, city officials said.
On Tuesday, Coney Island Hospital, at the tip of Brooklyn, was evacuated. Although one of its generators was still puttering along, another had long been underwater, and officials were reluctant to leave patients in such precarious conditions.
ABC News' Elicia Dover and Michael S. James contributed to this report.