For much of this past week, as a dangerous viral outbreak continued to rattle the world, officials seemed keen to offer reassurances. Chinese leaders urged people to get back to work. American officials said they saw no need to evacuate citizens from a quarantined cruise ship in Japan.

In a sign of how unpredictable the crisis still is, and how quickly officials have had to adapt their responses, both of those declarations had at least partly unraveled by Saturday.

Communist Party leaders said people returning to the Chinese capital would have to isolate themselves for two weeks, potentially delaying any economic revival. American officials announced that they would charter a flight to evacuate American citizens from the cruise ship, after citing heightened danger to those on board.

The number of confirmed cases of the coronavirus disease, named COVID-19, continued to climb on Saturday, and their geographic locations continued to spread. The virus claimed its first life outside Asia when an 80-year-old Chinese tourist died in France, according to the French health minister. It was the fourth death outside mainland China.

A day earlier, the outbreak also reached Africa for the first time, with Egypt reporting the continent’s first confirmed case.

On Saturday morning, the Chinese authorities reported 2,641 new cases and 143 deaths in the previous 24 hours. In all, more than 66,000 infections and 1,523 deaths have been confirmed.

The American Embassy in Tokyo, explaining the evacuation decision to American citizens on board the cruise ship on Saturday, acknowledged the rapid changes. “This is a dynamic situation,” the embassy said in an emailed letter.

The ship, the Diamond Princess, has been quarantined for more than a week at the port of Yokohama, after the coronavirus was diagnosed in a man who had disembarked days earlier in Hong Kong. About 3,700 passengers and crew members were aboard when the quarantine was imposed, including more than 400 Americans.

For days, United States officials had assured American passengers that evacuation was not necessary, even as more than 200 cases were diagnosed on board. On Feb. 8, the embassy told American passengers in a letter that “remaining in your room on the ship is the safest option to minimize your risk of infection.”

But Saturday’s letter made clear that the calculus had changed.

“To fulfill our government’s responsibilities to U.S. citizens,” the letter said, the U.S. government recommended “that U.S. citizens disembark and return to the United States.” Passengers who did not leave on the charter flight would not be able to return to the United States “for a period of time,” it added.

American officials also said previously that the American passengers would not have to be quarantined upon their return to the United States. But the embassy’s email on Saturday said the evacuees would need to be quarantined for two more weeks once they arrived.

While the letter did not explicitly give a reason for the change, an official with the Centers for Disease Control and Prevention suggested on Friday that the authorities had re-evaluated the ship’s conditions.

“The data coming out of Japan suggests there’s a higher risk among the people on the ship,” the official, Dr. Nancy Messonnier, said during a news briefing.

Sixty-seven new cases were announced aboard the ship on Saturday, the most in a single day since the quarantine began.

The American government’s announcement seemed to trigger a chain reaction among other countries. Minutes after the United States Embassy’s letter was sent, the Australian Embassy in Tokyo sent its own email to its citizens aboard the Diamond Princess, citing the American evacuation plans and assuring Australians that it was “examining options.”

The Italian foreign minister also said on Saturday the country would do what was necessary “to protect our citizens” aboard the ship.

Within China, a flurry of new announcements reinforced the government’s continuing efforts to recalibrate its balance of economic and public health concerns.

The mandatory two-week self-quarantine for people returning to Beijing was announced late on Friday evening on the website of Chinese state-run television. Millions of migrant workers who power China’s economy had left urban centers to celebrate the Lunar New Year holiday last month.

Those who did not comply with the rules would “be held accountable according to law,” according to a text of the order released by state television.

But the policy, issued by Communist Party officials at the municipal level, seemed at odds with the message from Chinese national officials this past week. They had urged local officials to get businesses up and running again, and to help factories eliminate bureaucratic hurdles.

Mr. Xi, at a meeting of the Communist Party’s top leadership on Wednesday, said government officials at all levels should “strive to achieve this year’s economic and social development goals and tasks,” according to a summary of his remarks by state media.

After the Beijing restrictions were announced, some on Chinese social media observed that workers had already been streaming back to the capital for days, and they wondered how effective the new rules would be.

It was not the first time that Chinese officials had sent mixed signals about their desire to get people back to work. The same day that a top economic official urged factories to restart, a national health official said that the return of workers to major cities could foster new outbreaks in populous provinces with high populations of migrant factory workers.

In another possible hurdle to economic revival, a top Chinese banking official said on Saturday that commercial banks must disinfect and stash any cash they collect before releasing it back to customers.

Behind it all is uncertainty, and increasing diplomatic tension, about the scope of the outbreak.

While the World Health Organization has praised China’s response to the crisis, American officials in recent days have privately expressed doubts about whether China is underreporting cases, as well as about the official timeline for the first infections.

Chinese officials have been adamant that they have been transparent. On Friday, Wang Yi, the Chinese foreign minister, attacked what he called some countries’ “overreaction” to the outbreak.

“We have the confidence, capability and determination to prevail over the virus at an early date,” Mr. Wang said in an interview with Reuters.

Still, the Chinese authorities have acknowledged the difficulty in knowing the outbreak’s precise scale. On Thursday, officials added more than 14,800 new cases to the tally of those infected, the largest one-day increase recorded so far. They attributed the jump to a change in the way they diagnosed confirmed cases.

The United States will also widen its search for possible infections: American health officials in five cities will begin testing some people with flulike symptoms for the coronavirus, according to Dr. Messonnier of the C.D.C.

The constant changes have left people caught in the middle of the outbreak confused and frustrated.

Rachel Torres, 24, a newlywed on the cruise ship quarantined in Japan, said that she and her husband, Tyler, would take the evacuation flight, though they were frustrated that it had not been offered earlier.

Gay Courter, 75, an American novelist from Crystal River, Fla., near Tampa, said she and her husband, Philip, would also leave the ship despite the unexpected quarantine period.

“This is what we’ve been asking for, because we never felt quarantine on this ship was safe,” she said.

Elian Peltier, Edward Wong and Elaine Yu contributed reporting. Claire Fu contributed research.