NEW YORK/ LOS ANGELES (Reuters) - The U.S. government raced on Tuesday to build hundreds of makeshift hospitals near major cities as healthcare systems were pushed to capacity, and sometimes beyond, by the coronavirus pandemic.

Even as millions of Americans hunkered down in their homes under strict “stay-at-home” orders, the death toll, as tallied by Reuters, shot up by more than 850 on Tuesday, by far the most for a single day.

Nearly half of the new fatalities were in New York state, the epicenter of the pandemic despite closed businesses and deserted streets. New York City Mayor Bill de Blasio pleaded for immediate reinforcements in the country’s biggest city from the Trump administration.

“This is the point at which we must be prepared for next week, when we expect a huge increase in the number of cases. What I asked very clearly, last week, was for military medical personnel to be deployed here,” de Blasio said at the Billie Jean King National Tennis Center in Queens, where a field hospital was being hastily built.

The sports complex is home to the U.S. Open Tennis Championship, set to begin on Aug. 24. It remains on the calendar despite reports that Wimbledon, the sport’s most prestigious event, is unlikely to go forward as scheduled in June. The U.S. Open and Wimbledon are two of the four Grand Slam tennis tournaments.

De Blasio, a Democrat who last year sought his party’s presidential nomination, said he had asked the White House for an additional 1,000 nurses, 300 respiratory therapists and 150 doctors by Sunday.

“DEBILITATING AND EXHAUSTING”

Nearly 3,900 people have already died from COVID-19, the illness caused by the coronavirus, in the United States, more than the 2,977 who died in the Sept. 11, 2001, attacks. The total confirmed U.S. cases rose to 187,000.

White House medical experts say 100,000 to 240,000 people could ultimately perish from the respiratory disease in the United States, despite unprecedented orders by state and local governments largely confining Americans to their homes.

In addition to the rules issued by at least 30 states, President Donald Trump, reversing course, said this week that most businesses and schools should remain shut at least through the end of April. Trump, speaking at the White House on Tuesday, said the next two weeks would be “very, very painful” for the country.

“We want Americans to be prepared for the hard days that lie ahead. We’re going to through a very tough two weeks and then, hopefully, as the experts are predicting ... you’re going to be seeing some real light at the end of the tunnel,” the president said.

The U.S. Army Corps of Engineers sought hotels, dormitories, convention centers and large open spaces to build as many as 341 temporary hospitals, Lieutenant General Todd Semonite told the ABC News “Good Morning America” program. The corps has already converted New York City’s Jacob Javits Convention Center into a 1,000-bed hospital.

In Los Angeles, the city’s massive convention center was being converted to a federal medical station by the National Guard, Mayor Gil Garcetti said on Twitter. In California, the most populous U.S. state, the number of coronavirus patients has surged over the past few days, with more than 7,600 cases confirmed as of Tuesday and 150 deaths.

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Connecticut Governor Ned Lamont said on Tuesday the U.S. Strategic National Stockpile of medical supplies was now empty and the state was “on its own” trying to obtain medical equipment to fight the pandemic.

A Dutch cruise ship with confirmed cases of the virus and four fatalities on board sought permission to dock in Florida, even as Governor Ron DeSantis said the state could not afford to take on any additional patients.

The pandemic has taken a toll on doctors, nurses and other healthcare workers, who are overworked and lack the medical devices and protective gear needed.

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“The duration itself is debilitating and exhausting and depressing,” New York Governor Andrew Cuomo told a news conference.

The governor said his brother, 49-year-old CNN anchor Chris Cuomo, had tested positive for the coronavirus on Tuesday and would host his nightly show from his basement to avoid infecting family members or others.

U.S. coronavirus-related deaths still trail those of Italy and Spain, which have more than 11,000 and 8,000 reported fatalities, respectively. China, where the outbreak is believed to have originated, has reported 3,305.

Worldwide, there are now more than 800,000 cases of the highly contagious illness caused by the virus and more than 40,000 deaths reported. (Graphic: tmsnrt.rs/2w7hX9T)

An intensive-care-unit nurse at a major hospital in Manhattan said he had been shocked by the deteriorating condition of young patients with little or no underlying health issues.

“A 28-year-old, healthy fellow ICU nurse is currently so sick that he has difficulty walking up a single flight of stairs without gasping for breath,” said the nurse, requesting anonymity because he was not authorized to speak to the media.