BEIJING — As officials grow increasingly fearful about their ability to contain the fast-spreading outbreak of a novel coronavirus, this metropolis recorded its first death on Monday, hundreds of foreign nationals prepared to flee the country, and the U.S. government warned Americans to avoid all nonessential travel to China and planned to boost airport staff to screen nearly all passengers from there.

In a rare public mea culpa, a Chinese official said Monday that the government had mishandled the early stages of the crisis, which has claimed at least 100 lives and infected more than 4,400 people. Wuhan Mayor Zhou Xianwang, speaking with Chinese state broadcaster CCTV, said his city did not release “timely and satisfactory” information at the start of the epidemic, and he appeared to blame higher-ups in his chain of command.

“I hope everyone can understand that this is an infectious disease, and infectious diseases must be disclosed according to law,” he said. “We can only disclose information after we receive authorization.”

The mayor said 5 million people have already left his city, some before and some after the official quarantine. Meanwhile, more than 700 miles away, Beijing recorded its first death from the outbreak, according to the city’s health commission. A 50-year-old man who visited Wuhan on Jan. 8 developed a fever when he returned home a week later and died Monday — one of the pathogen’s younger victims. Seven other cases of illness in Beijing have been confirmed so far.

Late Monday, a top U.S. health official criticized Chinese authorities for not inviting U.S. and other international investigative agencies to join them in researching the new virus. While China has been more transparent than it was during the 2003 SARS outbreak, U.S. officials are still getting their information through press briefings rather than from direct transfer of scientific data, said Anthony S. Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases.

Fauci pointed out that China’s health minister, Ma Xiaowei, said publicly Sunday that the virus could be transmitted by an infected person even before symptoms appear.

“We really need to know what is the scientific basis of saying the virus is spread by someone who doesn’t have any symptoms,” Fauci told The Washington Post. “That was a major potential game-changer that gets spoken to us in a press briefing. We should have seen the data.”

This could affect how the U.S. screens people traveling from China.

“If people can be transmitting and infecting without any symptoms, that has a major impact on how you screen people,” he said.

Amid growing alarm about the disease’s fast spread, the U.S. Centers for Disease Control and Prevention is boosting staffing at 20 U.S. airports that have quarantine facilities. Vice President Pence said Monday that those airports receive 90 percent of airline passengers from China. Previously, passengers from Hubei province were screened and tested at five airports if they showed signs of fever or respiratory illness or have been in contact with a sick person, the CDC said. The expanded effort will take effect in coming days.

Epidemiologists around the globe raced to understand how the virus spreads, how long it incubates before making a person ill, whether it can be contagious even when the person is asymptomatic, and how lethal it is. They said the public should not assume the worst about this outbreak. This virus does not appear to be as deadly as SARS or MERS, two similar coronaviruses that made the jump from animals to humans earlier this century and that were ultimately contained. The victims so far of the new coronavirus have overwhelmingly been over 60 or already ill from other causes.

In the United States, 110 people in 26 states are being tested for possible infection, but only five so far — all people who traveled from Wuhan, the capital of Hubei province in central China — are confirmed to have the infection, the CDC said Monday. No one in the United States has died, and there is no known case yet of the virus spreading within the country.

“We understand people may worry about the new #coronavirus,” CDC Director Robert R. Redfield tweeted Monday. “In today’s connected world, an outbreak anywhere can be a risk everywhere. Risk is dependent on exposure. 2019-nCoV is not spreading in the US at this time. CDC continues to believe the risk to the US public is now low.”

The five confirmed cases are in Southern California, Chicago, Arizona and Washington state. Infections also have been confirmed in France, Germany, South Korea, Japan, Nepal, Thailand, Cambodia, Singapore, Vietnam, Taiwan, Canada and Sri Lanka.

The CDC increased its travel warning to a Level 3 Monday — its highest alert level — urging U.S. citizens to avoid all nonessential travel to China because of the outbreak. The warning says those who travel should avoid all contact with sick people, animal markets and products that come from animals, and wash their hands often with soap and water for at least 20 seconds.

Among the most urgent questions is whether the unprecedented quarantine around the outbreak’s epicenter, in Hubei, will be effective. Widespread suspicions on Chinese social media that government officials mishandled the early stages of the crisis were fanned dramatically on Monday by the Wuhan’s mayor’s interview.

Dong-Yan Jin, a professor of molecular virology and oncology at Hong Kong University’s School of Biomedical Sciences, said Chinese authorities missed the critical moment to control the epidemic: before the Lunar New Year travel rush began a week ago.

“There was a lack of transparency in Hubei and an unwillingness by local governments to face the music; now, they tend to overcompensate,” Jin said. “You cannot expect that to work miracles and stop the outbreak.”

Viruses can mutate during an outbreak and become more or less deadly, but genetic analysis of the virus from people infected shows no sign of mutation, said Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, speaking to reporters Monday.

As early as Tuesday, a flight is scheduled to evacuate those working for the U.S. Consulate General in Wuhan, along with other U.S. citizens in the city who are willing to leave. In a statement, the U.S. Embassy in Beijing cautioned, “[we] anticipate that there will be limited capacity to transport private U.S. citizens,” and that “priority will be given to individuals at greater risk from coronavirus.”

The flight back to the United States will land in Ontario, Calif., after refueling in Anchorage, according to a U.S. government official who spoke on the condition of anonymity because they were not authorized to discuss the details. The U.S. citizens aboard the plane will be evaluated before they board, during the flight and after they arrive in the United States, the official said. Once they arrive in California, they will be isolated for 72 hours and monitored, the official said.

Many other countries, including Japan, France and Sri Lanka, are seeking to evacuate their citizens from the coronavirus epicenter of Wuhan. The German government said Monday that it was still “considering” an evacuation.

Monika Sethuraman, a PhD student from India, described Wuhan as a “ghost town” when she stepped out of her university dormitory for the first time in four days Monday to stock up on supplies. She bought vegetables to last for three weeks. She said the university has asked students to remain confined to their rooms and distributed thermometers.

“Every day before noon, we have to check our temperature and register it on a university portal,” she said.

Debesh Mitra, a postdoctoral scientist at another university in the city, described the situation as “grim.” He said he had avoided leaving the campus for fear of contracting the virus. “We really want to come back [to India] at the earliest,” he said. “All our families are very worried.”

Global markets took a sharp downturn Monday as investors grew increasingly anxious about the swift spread of the coronavirus beyond China. The Dow Jones industrial average plunged 454 points, or about 1.6 percent. The Standard & Poor’s 500 and Nasdaq indexes were also down 1.6 percent and 1.9 percent, respectively.

“Stock markets are selling off this morning on fears that the coronavirus might be harder to contain than previous viral outbreaks,” said Ed Yardeni, president of Yardeni Research.

A reliable estimate of the lethality and infectiousness of the new virus — which experts have been referring to simply as “the novel coronavirus” and which has the temporary technical name of “2019-nCoV”— would require a better understanding of how many people have been infected so far. Many infected by the virus may have thought they simply had a cold.

Officials in the United States and China have said the best estimate so far of the coronavirus’s contagiousness is that it will spread to between 1.5 and 3 people from every person who is sick. That is much less transmissible than measles, for which the rate can be as high as 18. But any number above one is problematic; only by lowering the rate below one can an outbreak be suppressed over time.

An American epidemiologist who helped China contain the 2003 SARS virus plans to return Tuesday to assist his Chinese counterparts with their response. Ian Lipkin, director of Columbia University’s Center for Infection & Immunity, said it’s still too early to predict how widespread or deadly the outbreak will turn out to be.

“Until we have a handle on all of these issues, it’s very difficult to make predictions about the outbreak,” Lipkin said.

He added that putting the outbreak in the context of other prevalent diseases was key: “It’s fair to say that every year, there are 30,000 to 40,000 people who die of flu in the United States. It is very unlikely that this will ever reach the level that we annually lose to flu.”

Denyer reported from Tokyo. Sun and Achenbach reported from Washington. Niha Masih in New Delhi, Rick Noack in Berlin, and Rachel Siegel, Siobhán O’Grady, Adam Taylor, Yasmeen Abutaleb and Lenny Bernstein in Washington contributed to this report.