“If you’re employed by us, it is expected you can be reassigned to an area of need,” David Battinelli, Northwell’s chief medical officer, said in an interview. Those who do not agree will be furloughed without pay, he said.

Dr. Battinelli said clinical staff would be reassigned based on their skills and comfort level. All elective surgeries have been canceled across the Northwell network, and only 20 percent of its patients, he estimated, were coming in for non-coronavirus emergencies like heart attacks, strokes and injuries.

Conference rooms, lobbies and some cafeterias were being converted to intensive care units; the network plans to expand its bed capacity by 60 percent.

“Obviously that puts pressure on trying to find staff to support those patients,” said Terry Lynam, a Northwell spokesman. “That’s the biggest concern — to try to get additional staffing.”

On Thursday, Mayor Bill de Blasio called for a national draft of doctors and medical workers to be sent to places where the virus has hit hardest, starting with New York. Some hospital systems had already been pleading for help from outside their networks. On Wednesday, NewYork-Presbyterian Hospital put out a call on Twitter for doctors and nurses, as it tries to expand intensive care units and emergency rooms in its hospitals.