BEIJING — Health authorities in the prosperous province of Zhejiang had finally lowered the alert level from one to two after six weeks, satisfied their draconian measures to contain the novel coronavirus had worked.

Once the hardest-hit Chinese province beyond Hubei, coastal Zhejiang had placed 30 million people under lockdown, but there were no new cases reported in nine days in the key export and manufacturing base.

Then Wang, a 31-year-old waitress who had been working in the northern Italian city of Bergamo, came home to Qingtian county, west of the city of Wenzhou.

She had developed a cough, headache and diarrhea about a week before the flight, but nevertheless went to Milan and boarded a plane for Moscow, settling into seat 22F. Traveling with five others from the same restaurant, she changed planes in Moscow and took off for Shanghai. This time, she sat in an aisle seat.

When Wang, whom authorities have identified only by her family name, arrived in China, she was immediately put into quarantine. On Sunday, she tested positive for the novel coronavirus that causes the disease named covid-19. Seven others who worked in the Bergamo restaurant and flew back home were diagnosed this week, the Qingtian government said on its WeChat social media account.

This is China’s new coronavirus challenge.

Having largely contained the virus at home — the number of new infections reported each day has fallen to barely 100, almost all in Hubei province — China now faces the prospect of imported infections as the outbreak rages beyond its borders.

China thought that once it had contained the epidemic, that would be the end of it, said Zhang Wenhong, director of the department of infectious diseases at Shanghai Huashan Hospital, affiliated with Fudan University. But now, more cases are emerging abroad than in China — and they’re starting to come back.

“This is a bad sign and very worrisome,” Zhang told China News. “It will bring difficulties to China’s outbreak control.”

More than 6,700 passengers had arrived in China with coronavirus infections by the end of Tuesday, and 75 were confirmed as infected, General Administration of Customs said on Wednesday. 

China’s Communist Party appears mindful that other governments might lack the techno-authoritarian tools to shut down the spread like it did. Authorities are taking measures to prevent people who have traveled to new hotspots — South Korea, Iran, northern Italy and Japan — from bringing the disease back.

The southern province of Guangdong, a manufacturing and export hub that borders Hong Kong, and the financial center of Shanghai have stipulated that all travelers arriving from severely affected countries must quarantine themselves for 14 days.

Beijing, which already has a 14-day quarantine rule for all arrivals, explicitly singled out the four hotspot countries during a briefing this week. Two of the three new cases confirmed in Beijing on Tuesday were imported, one from Iran and the other from Italy.

Zhejiang is particularly at risk of cases from Italy because the Wenzhou area has historical trading links with the European country, which has reported more than 2,200 cases and dozens of deaths. There are about 200,000 Chinese from Wenzhou and Qingtian living in Italy, most working in the restaurant business, the Zhejiang Daily reported this week.

During the initial phase of the outbreak, Chinese citizens living in Italy donated 10,000 masks, 300 protective suits and 240 pairs of goggles to Wenzhou residents.

As the epidemic evolves, Wenzhou residents are returning the favor. The Wenzhou Eyewear Industry Association sent boxes of protective glasses to Italy this week — with “Wenzhou per Italia” and a picture of the Leaning Tower of Pisa on the boxes.

Likewise, the western province of Ningxia, home to many members of the Hui Muslim minority, appears susceptible to imported cases from Iran. Last week, two people returned from Iran to Ningxia with the virus, while Beijing found two people who had been in contact with one of the Ningxia patients were also infected.

Chinese officials are in an awkward situation. Early in the outbreak, China’s Foreign Ministry lashed out at the United States for “overreacting” and “sparking panic” when Washington warned travelers against visiting China and evacuated its consulate in Wuhan.

Now, Zhejiang authorities are telling their citizens abroad to “minimize” travel. Traveling is the easiest way for infections to be transmitted, so staying home is the “best form of protection,” the Qingtian local government said in a notice to overseas Chinese.

“For the sake of your family’s health and safety, please strengthen your precautions, carefully decide on your travel plans and minimize mobility,” it posted on its WeChat account.

But in Beijing, central authorities have been encouraging people abroad to come home, saying it “attaches great importance to the health of Chinese citizens” in countries such as South Korea, Japan, Italy and Iran.

“If the situation in those countries worsens, the Chinese government will take further actions to help bring them back to China,” China Daily quoted Cui Aimin, director general of the Foreign Ministry’s Department of Consular Affairs, as saying.

Concerned that its citizens will catch the coronavirus abroad, China has started evacuating people from virus-stricken areas.

Two planes arrived in Hangzhou from Milan this week, and China sent two charter planes to Iran to collect citizens, since direct commercial flights have been canceled. The first arrived Wednesday in the city of Lanzhou, near Ningxia province.

Priority was given to students stranded in the holy city of Qom, where the coronavirus infections are the most serious in the country, the Global Times reported. The remainder were employees or businesspeople.

“Ninety percent of the Chinese I know in Iran want to go home now,” a Chinese man living in Tehran, named as Lao Qi, told the Global Times. “They are worried about the rapid development of the epidemic in Iran and the lack of strong anti-epidemic measures by the local government and the lack of awareness among the Iranian public,” he said.

Tiffany Liang in Hong Kong and Wang Yuan contributed to this report.