HONG KONG—The city of 11 million where China’s deadly coronavirus outbreak originated is now under total quarantine, a massive lockdown that marks a dramatic shift from the Chinese government’s previous reaction, which was focused on limiting what the public could learn about the spread of the disease.

But the move comes after the virus has spread far and wide, including at least one case in the United States. Sixteen people who came into contact with the country’s sole confirmed coronavirus patient, in Washington State, are being monitored for pneumonia symptoms.

It is still far from clear that Beijing is revealing all that it knows about the disease and its transmission at a moment when hundreds of millions of people are expected to be on the move as the Chinese New Year approaches on January 25.

Wuhan, a major city in central China and a key transport hub, is now cut off from the rest of the country. Flights out of the city have been canceled, as have outbound trains. Public transportation in Wuhan has been shut down. Before the lockdown took effect, many people rushed to train stations and bus depots to purchase any tickets that would take them out of the city. Now soldiers of the People’s Liberation Army prevent them from even entering those buildings. Police vans are parked in front of toll booths on highways leading out of the city, turning back anyone who attempts to get out.

The Wuhan government requires all who remain within the city limits to wear face masks when they are in public places. Pharmacies are limiting sales, allowing customers to purchase only one mask at a time. Hospitals are turning away people who are requesting health tests because of the lack of trained personnel to handle the volume. At least 14 medical workers who were tending to the sick have fallen ill themselves. One doctor who has recovered believes that he became infected after the virus was transmitted through his eye.

“ The front page of People’s Daily, the official newspaper of the ruling Chinese Communist Party, had no mention of the virus. ”

Following the complete quarantine of 11 million people in Wuhan, smaller cities in the same province, Hubei, are doing the same. Huanggang, a city east of Wuhan with a population of 7 million, will suspend all public transport and close all public venues beginning at midnight local time. Ezhou, a smaller city south of Huanggang, is also halting all train and bus services for its 1 million residents until further notice. Both cities share borders with Wuhan.

Some large-scale events in Beijing, the nation's capital, have been canceled by the city government. These include temple fairs that are part of Lunar New Year celebrations.

The novel coronavirus, or CoV, was first detected in Wuhan in mid-December. It causes pneumonia-like symptoms and can be deadly, particularly for children and the elderly. Scientists believe that the virus may have originated in bats or snakes before making the leap to human hosts, and it can be transmitted from human to human. (Snakes, which hunt bats, are consumed as food in some parts of China, and they have been sold at the market where the first batch of patients worked.)

CoV, like its cousins SARS and MERS, has an incubation period of up to two weeks, meaning anyone who is infected may not present symptoms until nearly half a month later—at which point the infection may have traveled around the world.

On Wednesday, Chinese officials put the official death toll at 17, nearly doubling the nine that were announced just hours earlier. All 17 deaths were in Hubei, the province where Wuhan is the capital. In mainland China, there are 571 confirmed cases of infection, with another 11 in Hong Kong, Macau, Taiwan, Thailand, Japan, South Korea, and the United States. The Chinese government has acknowledged that infections are present in 25 of its provinces and municipalities—in other words, the coronavirus has spread all over the country.

Estimates by experts tell a more dire story. Scientists at the MRC Centre for Global Infectious Disease Analysis at Imperial College London believe at least 4,000 people have succumbed to the coronavirus. Doctors in Wuhan who spoke to Chinese media outlet Caixin believe the number to be even higher, possibly at 6,000.

There are persistent concerns that the Chinese government is suppressing information about the scale of the outbreak.

The front page of People’s Daily, the official newspaper of the ruling Chinese Communist Party, made no mention of the virus, infection numbers, death tolls, or the situation in Wuhan on Thursday morning. Instead, the headlines referred to various recent activities of Chairman Xi Jinping in other areas while paying tribute to his “leadership.”

Some social media posts about the outbreak have been removed from various platforms. More tellingly, Zhong Nanshan, the head of a team of high-level medical professionals at China’s National Health Commission, is no longer speaking to the media. (During the SARS epidemic of 2002–03, Zhong was the head of the Guangdong research institute for respiratory diseases. He is one of the top respiratory health experts in the country.)

There may already be a scapegoat in the making. Wuhan’s mayor, Zhou Xianwang, was featured on state television, where he tried to explain his government’s slow response to the coronavirus outbreak. The Chinese public’s anger is temporarily focused on Zhou, and there are public, open calls for his resignation, while many have also expressed sympathies toward the people of Wuhan, where the quarantine may last for two months.

“ The World Health Organization may declare a 'public health emergency of international concern,' a move that its secretary general said he takes 'extremely seriously.' ”

At the moment, there is just the one confirmed infection in the United States—a U.S. citizen who returned to the country after a trip to central China. He was diagnosed in Seattle and was admitted to a hospital in Everett, Washington, where doctors are using robots to treat him.

Officials at the Centers for Disease Control have said the coronavirus originating in Wuhan carries low risk for the American public. However, a vaccine may take months to develop—scientists in the United States and China are working on this—and it may be more than a year before it is available to the public.

Airports around the world are stepping up health screenings for incoming passengers, though the relatively long incubation period means these measures may not hinder the spread of the virus.

Late Wednesday in a brief press statement, World Health Organization Secretary General Tedros Adhanom described the situation as “evolving and complex.” While diplomatically praising the “detail and depth of China’s presentation,” he also noted, “we need more information.” The WHO may yet declare a “public health emergency of international concern,” a move that the secretary general said he takes “extremely seriously.”