China on Monday announced that travelers from overseas would no longer be required to enter quarantine upon arrival, in one of the country’s most significant steps toward reopening since the coronavirus pandemic began.

From Jan. 8, incoming travelers will be required to show only a negative polymerase chain reaction, or P.C.R., test within 48 hours before departure, China’s National Health Commission said. Limitations on the number of incoming flights will also be eased.

The travel restrictions had isolated the world’s most populous country for nearly three years. Foreigners were essentially barred from entering China in 2020, and even when they were allowed back in months later, it was generally only for business or family reunions.

Even some Chinese nationals were unable to return home initially, and travelers allowed to enter were required to undergo extensive health screening and quarantine at their own expense — sometimes for as long as two months.

The announcement on Monday was the latest reversal in China’s “zero Covid” approach to the virus, which for years saw Beijing seek to eliminate infections. But the policy, which involved harsh and prolonged lockdowns of hundreds of millions of people, crushed the economy and stirred public discontent.

In November, after a fire led to the deaths of 10 people in the Xinjiang region, with many people suspecting that a Covid lockdown had hampered rescue efforts, protests erupted across the country. It was one of the boldest and most widespread outbreaks of dissent in decades. Within days, the government began loosening restrictions.

The easing of travel restrictions “basically signals the final end of zero Covid,” said Yanzhong Huang, a senior fellow for global health at the New York-based Council on Foreign Relations. Though China had relaxed many of its zero-Covid domestic policies this month — scrapping regular mandatory tests for urban residents and allowing home quarantine for the infected, for example — it had held on to its international limitations.

The new measures do not amount to China’s throwing open its borders, however. Many details remained unclear. The government has not said when it will resume issuing tourist visas — all such visas that were valid at the start of the pandemic have been canceled. Officials said that they would “further optimize” the ability of foreigners to apply for visas for business, study or family reunions, without offering specifics.

Chinese officials also did not say how many flights would be allowed to enter the country. In November, the number of international flights to China was 6 percent of what it was in 2019, according to the flight tracker VariFlight.

China will also allow its citizens to resume traveling abroad for leisure in an “orderly” fashion, officials said. During the pandemic, the government stopped issuing or renewing Chinese nationals’ passports except in limited circumstances, and in May it said it would “strictly restrict nonessential exit activities.”

The end to the international Covid quarantine was part of a broader announcement on Monday that China would downgrade its classification of the coronavirus. Previously, the government treated Covid-19 as a Category A infectious disease, on par with cholera or the bubonic plague. Under that categorization, officials had to put in place extensive restrictions to control the spread, including lockdowns and quarantines. Going forward, Covid will be treated as a Category B disease, which includes AIDS and bird flu.

That change will further formalize China’s shift away from zero Covid domestically, Dr. Huang said. While the earlier easing of restrictions had left local officials some leeway to decide how fast to reopen, Beijing was now signaling to officials nationwide that they should prioritize reviving the economy over disease control, he said.

It was unclear, however, just how soon international travelers would be willing to visit China, and how much the economy would benefit from it. The recent loosening of restrictions has led to an explosion in infections. Many older Chinese are not vaccinated or have received only two shots. The number of infections and deaths is also unclear, as mass testing in the country has ended and China counts Covid deaths differently from most of the rest of the world. But reports of overwhelmed hospitals and funeral homes are widespread.

At a news conference on Sunday, an official in Zhejiang Province, home to about 5 percent of China’s population, estimated that there were more than one million new Covid cases a day there.

Dr. Huang said that while China had pursued zero Covid for too long, he was now worried that policymakers had swung too quickly in the opposite direction.

“I’m afraid the mitigation strategy that is supposed to be focusing on the elderly and the vulnerable will be relegated to the back burner,” he said.

The speed, and shock, of China’s Covid pivot was reflected on its social media platforms, where users greeted the news of the rollback on Monday with a mix of disbelief and elation. Some celebrated the fact that Chinese students studying overseas would be able to return more easily to visit their families. In the minutes after the announcement, Chinese news media reported, searches for international plane tickets on one travel platform soared.

Others said, however, that they could not bring themselves to be happy about the changes, given the scale of China’s outbreak and deaths. Others noted that less than one month earlier, huge swaths of cities, including Beijing, had been under lockdown.

Claire Fu and Amy Chang Chien contributed reporting.