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As the number people killed by the coronavirus in the United States topped 10,000 by Monday night, the country's top medical officials warned that the worst was yet to come.

The number of cases has ballooned to at least 364,167 — nearly three times higher than in the second-worst hit country, Spain — with 10,772 people killed as of 7:30 p.m. ET, according to NBC News' tracker.

At the center of the outbreak in the U.S., New York Mayor Bill de Blasio said critical medical supplies and personnel have been secured but warned that the magnitude of the crisis equals that of the 1918-19 flu and the Great Depression.

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As of Monday night, the city had recorded at least 2,738 deaths due to the virus, according to the Health Department.

While 2,865 ventilators and 1,780 more breathing assistance machines had been distributed through the city, de Blasio said, it needs 1,000 to 1,500 more ventilators by Sunday.

A patient arrives at Wyckoff Hospital in the Bushwick section of Brooklyn, N.Y., on Sunday, April 5, 2020. Bryan R. Smith / AFP - Getty Images

Surgeon General Jerome Adams urged the nation to stay home and practice social distancing Sunday, saying this week would be this generation's "Pearl Harbor moment."

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"It's going to be the hardest moment for many Americans in their entire lives," Adams said NBC' News' "Meet the Press," adding: "And we really need to understand that if we want to flatten that curve and get through the other side, everyone needs to do their part."

Meanwhile, the country's top infectious diseases expert, Dr. Anthony Fauci, acknowledged that the nation is "struggling" to get the outbreak under control.

In an interview Sunday on CBS News' "Face the Nation," Fauci said: "Things are going to get bad, and we need to be prepared for that."

A man wearing a mask amid concerns over the spread of the coronavirus travels on a train in Tokyo on Monday, April 6, 2020. Philip Fong / AFP - Getty Images

Veterans across the country are also losing their lives to the virus, accounting for 103 deaths as of Sunday evening, according to the Department of Veterans Affairs. Nearly 25,000 tests have been administered to veterans, revealing 2,699 confirmed cases — an increase of 183 from the previous day.

Overseas, Japan is also bracing for the worst. Prime Minister Shinzo Abe was expected to declare a state of emergency as early as Tuesday morning as the number of cases surpasses 3,600, according to local media reports.

The Tokyo Medical Association issued a statement Monday calling on Abe to issue the declaration to make necessary resources available for the country's medical system. The statement follows mounting criticism from business owners and politicians that the country has not reacted quickly enough.

U.S. Forces Japan, meanwhile, declared a health emergency Monday for its bases in the Kanto region, which includes Tokyo, in response to the rise in cases.

In Italy — where 15,887 people have died, the most in the world — the latest data showed signs that a peak may have been reached with three days of declining daily death tolls. The country reported 525 more deaths Sunday, a big drop from the height of 969 on March 27.

A child jumps rope in a courtyard in Milan on Monday, April 6, 2020, as the spread of the coronavirus disease continues. Daniele Mascolo / Reuters

The country's health minister, Roberto Speranza, said that Italy is exploring options to ease lockdown restrictions but that a return to normal life is still far off and social distancing rules will likely remain to prevent a rebound in cases.

Also appearing on "Meet the Press," Italian Prime Minister Giuseppe Conte discussed the "devastating pain" the country has experienced through the loss of life and the weeks of social isolation.

"We are asking our people a great sacrifice. I'm aware of it. But it is the only way to defeat the pandemic altogether. The more we respect the rules, the sooner we will get out," he said.

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The number of new cases in Spain also appears to be slowing, according to Health Minister Salvador Illa. Sunday saw a 5 percent increase in new cases, compared to a daily rate of 22 percent three weeks ago.

Spain is among the hardest-hit countries, with 12,641 deaths and 131,646 cases. Illa said the country continues to face "very tough weeks ahead" as the number of patients going into intensive care reaches "especially worrying" levels.