NUSA DUA, Indonesia — The family from Shanghai was vacationing in Singapore last month when they learned that the new coronavirus had arrived there from China.

So they packed up and flew to the world’s largest country yet to report a single case of the deadly virus: Indonesia. They landed in Bali, a major destination for Chinese tourists, on Jan. 30 and have no plans to leave.

“People in Bali treat us nicely and are friendly,” said Eva Qin, 36, who is traveling with her mother, husband and son. “We weren’t given any health test.”

Health experts have questioned why Indonesia has not yet reported a single case of novel coronavirus, even though officials were slow to halt nonstop flights from China. Indonesia receives about 2 million Chinese tourists a year, most of them in Bali.

China’s consul general in Bali said last week that about 5,000 Chinese tourists remained in Bali, including 200 from Wuhan, where the outbreak started.

Indonesia’s closest neighbors have all reported cases, including the Philippines, Singapore, Malaysia and Australia.

“So far, Indonesia is the only major country in Asia that does not have a corona case,” Indonesia’s security minister, Mohammad Mahfud MD, told reporters on Friday. “The coronavirus does not exist in Indonesia.”

None of the 285 people who were evacuated from Wuhan and are now in quarantine on the Indonesian island of Natuna have shown signs of the virus, he added.

Five researchers at the Harvard T.H. Chan School of Public Health concluded in a study last week that Indonesia and Cambodia, which has reported only one case, should quickly intensify its monitoring of potential cases. Based on a statistical analysis, the disease could have arrived in Indonesia already, the authors concluded.

“Many of the imported cases have been linked to a recent travel history from Wuhan, suggesting that air travel volume may play an important role for the risk of cases being exported outside of China,” the study said.

  • What do you need to know? Start here.

    Updated Feb. 10, 2020

    • What is a Coronavirus?
      It is a novel virus named for the crown-like spikes that protrude from its surface. The coronavirus can infect both animals and people, and can cause a range of respiratory illnesses from the common cold to more dangerous conditions like Severe Acute Respiratory Syndrome, or SARS.
    • How contagious is the virus?
      According to preliminary research, it seems moderately infectious, similar to SARS, and is possibly transmitted through the air. Scientists have estimated that each infected person could spread it to somewhere between 1.5 and 3.5 people without effective containment measures.
    • How worried should I be?
      While the virus is a serious public health concern, the risk to most people outside China remains very low, and seasonal flu is a more immediate threat.
    • Who is working to contain the virus?
      World Health Organization officials have praised China’s aggressive response to the virus by closing transportation, schools and markets. This week, a team of experts from the W.H.O. arrived in Beijing to offer assistance.
    • What if I’m traveling?
      The United States and Australia are temporarily denying entry to noncitizens who recently traveled to China and several airlines have canceled flights.
    • How do I keep myself and others safe?
      Washing your hands frequently is the most important thing you can do, along with staying at home when you’re sick.

The chairman of the Indonesian Red Cross, Jusuf Kalla, a former vice president of Indonesia, also said it was possible that the disease had already entered the country and that Indonesians might not recognize the symptoms as being coronavirus.

“Singapore has a tight system, but even there the virus got in,” he said. “It’s possible that there are infected people but here in Indonesia people think that it is only a regular fever or they think it is dengue fever.”

Mr. Kalla expressed concern about how prepared Indonesia was to handle the virus if it were to strike in remote parts of the archipelago nation where underfunded community health centers are the main health care provider. (Indonesia is the world’s fourth most populous country, with nearly 270 million people scattered across 6,000 inhabited islands.)

“Indonesia has many islands,” he said. “We have many port cities. They all have different capabilities. I think good hospitals in Jakarta can detect it. But what about the community health center in Flores? Or in Sulawesi? Surely the capability is limited.”

Indonesia’s health care system is considered underfunded by international standards, with insufficient facilities and too few doctors, nurses and midwives, according to a 2018 report by the World Health Organization.

But the W.H.O. country representative, Dr. Navaratnasamy Paranietharan, said Indonesia is doing its best to face the new coronavirus, including screening passengers at points of entry and equipping hospitals for the arrival of suspected or diagnosed cases.

“Indonesia is doing what is possible to be prepared for and defend against the novel coronavirus,” he said.

Health officials say they have tested nearly 50 suspected cases, which were all negative.

Thirty Chinese workers from a cement company in North Sulawesi were placed in 14-day quarantine last week after returning from a holiday visit to China, an immigration official said. None of them have come down with the virus, he said.

If patients with symptoms were arriving, they would have been detected, insisted Achmad Yurianto, secretary of prevention and control at the health ministry.

“We are not prepared to face a major outbreak, but we are prepared to prevent an outbreak,” he said. “We are not waiting for it to happen. We in fact have tightened prevention.”

Indonesia is experienced at monitoring travelers for illness, he said, because the country has long been on the lookout for another dangerous coronavirus, Middle East Respiratory Syndrome or MERS. About 1.4 million Indonesians go each year on pilgrimages to Saudi Arabia, where they can be exposed to MERS, he said, and they are screened on their return.

“We have experienced this many times,” he said. “Maybe other countries are not as diligent as Indonesia in dealing with this situation.”

Indonesia has three laboratories capable of testing for the new coronavirus, two in Jakarta, the capital, and one in Surabaya, Indonesia’s second-largest city, in East Java. The labs can test 1,200 samples a day, he said. Across the country, 100 hospitals have been designated as centers to handle suspected cases of the novel coronavirus.

Before airline travel between Indonesia and China was suspended on Feb. 5, there were 134 flights a week from China to Bali, bringing about 5,000 passengers a day.

The loss of new Chinese tourists could be devastating for the economy of Bali, which is highly dependent on foreign visitors. Still, some of the tourists already in Bali are doing what they can to stay.

China’s consul general in Bali, Gou Haodong, said many of the remaining Chinese tourists wanted to extend their visas rather than return home to possible quarantine or exposure to the virus.

More than 30 applied on Friday for tourist visas extensions, said immigration officials, who put the number of remaining Chinese tourists at 1,500, not 5,000.

Among those still in Bali this weekend were Johnson Guo and his family.

Mr. Guo, 42, a manager in an internet business in Guangzhou, said the family had been on holiday in Australia. But after the outbreak of the virus, they decided to extend their vacation and spend a week in Bali.

He said that they did not receive any health check on arrival, but that all of them were healthy.

“I worry about the virus,” he said, as he purchased 720 face masks to take back and donate to his hometown hospital when they were to return on Saturday. “But I have to return because I have to go back to work. And Guangzhou is not as bad as other areas in China.”

Two travelers from Shanghai, Song Yi and her friend, Yang Yujia, both 27, arrived in Bali in mid-January with eight friends.

“We didn’t have any health check because we have been healthy during the 20 days of our stay,” said Ms. Song, a banker, as they shopped for clothes at a mall near Kuta Beach.

Ms. Song said that the Balinese people had been very kind to them, but that their Chinese friends began avoiding each other because of fears about the virus and they soon went their separate ways.

After extending their stay in Bali, she said, they plan to return home next week.

“We decided to stay longer because we were afraid of the virus,” she said.