Across the U.S., where the number of infected topped 17,000, governors and public health officials watched the crisis in Europe with mounting alarm and warned of critical shortages of ventilators, masks and other gear at home.

In New York City, health officials told medical providers to stop testing patients for the virus, except for people sick enough to require hospitalization, saying testing is exhausting supplies of protective equipment.

As promised earlier in the week, President Donald Trump officially invoked emergency wartime authority to try to speed production of such equipment.

Countries frantically prepared for a deluge of patients in the coming weeks.

In Britain, the government asked 65,000 retired nurses and doctors to return to work. A convention center and hotels in Madrid were being turned into field hospitals for nearly 10,000 patients. France's military worked to build a makeshift medical center in the hard-hit town of Mulhouse. The U.S. readied military hospitals for civilian use.

Trump also announced the closing of the Mexican border to most travel but not trade. That brings it in line with the restrictions on the Canadian border earlier this week. The federal government also moved the income tax filing deadline from April 15 to July 15.

“We’re about to enter into a new way of living here in Los Angeles," Mayor Eric Garcetti said as California went into lockdown. “What we do and how we do it and if we get this right will determine how long this crisis lasts."

The streets of America's cities were quieter than normal, even in many communities not under lockdown.

In New York, Edjo Wheeler said he knew two people very sick with flu-like symptoms, which can indicate the coronavirus.

“That makes me walk around with my hands in my pocket to make sure I'm not touching things,' said Wheeler, 49, who runs a nonprofit art center. He added: “If everyone doesn't cooperate, it's not going to be effective."

At the Paramount Drive-in near Los Angeles, Forrest and Erin McBride figured a drive-in movie was one of the few ways they could responsibly celebrate their anniversary.

“We were like, what can we do? Everything’s closed,” Forrest said before a showing of “Onward.” “We were like, ‘Well, a drive-in theater is kind of like a self-quarantined movie date.’”

The virus has struck at the very identities of many countries: closing down cafes, restaurants and boulevard life in France, ending la dolce vita in Italy, shutting down England's pubs and the ceremonial changing of the guard at Buckingham Palace, damaging sales of tulips from Holland and shuttering the Statue of Liberty in the U.S.

Governments are trying to balance locking down residents with the need to keep food, medicine and other essentials flowing.

In Britain, the category of vital workers includes doctors, nurses and paramedics — and also vicars, truckers, garbage collectors and journalists. In New York, people venturing outside will have to stay at least 6 feet apart. And while they will be free to get some exercise to keep their sanity, there will be no "playing basketball with five other people,” Cuomo said.

“These provisions will be enforced,” the governor said. “These are not helpful hints.”

In Bergamo, the epicenter of the Italian outbreak, cemeteries were overwhelmed. Patients at the city's main hospital lined up in a narrow ward, struggling for breath as doctors and nurses moved swiftly from one beeping machine to the next.

“When the virus arrived here, there was no containment, and it spread through the valleys very quickly. ... Some said it was the normal flu. We doctors knew it was not,” said Dr. Luca Lorini, head of intensive care at the hospital, where nearly 500 beds were dedicated to people suffering severe symptoms. Eighty patients were in intensive care.

While the illness is mild in most people, the elderly are particularly susceptible to serious symptoms. Italy has the world’s second-oldest population, and the vast majority of its dead — 87% — were over 70.

Still, even younger people are at risk.

“You’re not invincible," WHO chief Tedros Adhanom Ghebreyesus warned them. He noted that many countries are reporting that people under 50 make up a “significant proportion” of patients needing to be hospitalized.

Some of the only good news came from Wuhan, the Chinese city where the outbreak began and where hospitals were struggling just weeks ago. For the second day in a row, no new infections were reported and only 39 cases were recorded nationwide, all brought from the outside, the government said.

With the crisis waning there, China has begun sending medical supplies to Europe.

The shutdown of whole swaths of the world economy took its toll, from millions of unsold flowers rotting in piles in Kenya to the slow emptying of the world's skies. Canada received 500,000 applications for unemployment benefits, versus 27,000 for the same week last year.

In the U.S., lawmakers and the White House sought to put together a $1 trillion economic rescue plan that would include the dispensing of relief checks of $1,200 for adults and $500 per child. The British government likewise unveiled a huge package under which the country for the time in its history would help pay the wages of those in the private sector.

Iran's official toll of more than 1,400 dead was rising quickly as well amid fears it is underreporting its cases.

As the virus strengthened its foothold in Africa, the continent's busiest airport, in Johannesburg, announced that foreigners will no longer be allowed to disembark.

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Associated Press reporters around the world contributed to this report.

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The Associated Press receives support for health and science coverage from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.