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Officials warned Tuesday that 400 new ventilators from the federal government will only allow public hospitals to handle a few more days of coronavirus caseload growth as the pandemic threatens to crush the Big Apple’s health care system.

“It’s going to buy us days. It’s not necessarily going to buy us weeks or months,” Mayor Bill de Blasio told reporters outside an Office of Emergency Management warehouse in Brooklyn. “It’s going to buy us days, given the growth of this crisis. Right now these ventilators are a help to our public hospitals but we need a lot more where that came from.”

The medical equipment, stacked on pallets, was loaded into trucks as de Blasio spoke. He said Monday that the city needs 15,000 ventilators to save the lives of coronavirus patients during the outbreak.

The shortage of machines is one of the most pressing issues confronting city and state officials as they race against time — and have ordered a statewide shutdown — to slow the disease’s spread to the point where the city and state hospital systems can cope.

Hizzoner was joined at the warehouse by the top doctor from Kings County Hospital, Dr. Steven Pulitzer, who said the equipment is critical to treating patients as the coronavirus attacks their lungs.

“What we’re seeing is that most patients who come into the hospital have a very quick course where they’re doing okay and then, in another day or two, they need ventilation,” Pulitzer said.

“The patient is basally suffocating without having this piece of equipment,” he added. “They come in and they have very low oxygen and this is the way we can give them the proper support that they need in order to get them through the critical part of their treatment.”

His colleague Dr. Samir Fahmy, head of pulmonary and critical care at the city-run hospital in Prospect-Lefferts Garden, went deeper.

“In the case of a patient with coronavirus, the lungs don’t work well because there’s fluid in the lungs. And the fluid prevents the oxygen from going from the lungs to the blood and then to other systems. You need a high concentration of oxygen, and the only way to provide it is with a ventilator,” Fahmy said.