Chengdu, China - Over the past few days, China has been reporting a slowdown in new coronavirus cases at home; except for Hubei, where the virus first appeared late last year, the vast majority of the provinces on the mainland have had no new infections.

But with more than 1,000 cases now being reported outside the country every day, China has a new worry: that Chinese nationals returning home from trips overseas, or foreigners visiting the mainland, will bring the infection with them.

So far, there have been 15 confirmed imported cases, nearly half involving a group of Chinese people who worked at a restaurant in the northern Italian city of Bergamo, as well as people travelling from Iran and a man who came from the United Kingdom via Hong Kong.

"We anticipated the beginning but failed to anticipate the end," said Dr Zhang Wenhong, director of Huashan Hospital's Department of Infectious Disease. "We thought as long as China controlled the situation, the world would be spared the disaster; but now that the outbreak in China is gradually under control, a mess is growing in the world."

Dr Zhang said it was worrying to see the sudden rise in confirmed cases around the world, which raised the risk of fuelling a new surge of cases in China.

The World Health Organization (WHO) raised its risk assessment for the global COVID-19 outbreak from "high" to "very high" on Friday, the highest alert level.

The WHO stopped using "pandemic," the previous highest alert, after the 2009 H1N1 global epidemic.

With the confirmation of community spread in a number of countries outside China, Beijing is stepping up its quarantine efforts aimed at those travelling to China from overseas.

Monitoring risk

"We currently do not have a special procedure for people arriving from other countries other than the 14-day quarantine," Wang Xue, an official at Chengdu Entry and Exit Inspection and Quarantine Bureau, told Al Jazeera.

"But if we have someone who arrives from high-risk areas, such as South Korea, Iran, or Italy, we have staff who will closely follow up with the passengers during their quarantine period to ensure there is no risk of virus transmission."

China imposed tough measures to try and bring the coronavirus outbreak under control but as infections rise outside China it worries travellers will become a source of new infections [File: Stringer/EPA]

Among all the countries battling COVID-19, Iran, with more than 2,000 infected and more than 70 deaths, has the potential to export a large number of confirmed cases back to China. Ties between the two countries have expanded as US-led sanctions squeezed Iran's economy.

More than 700 Chinese students are studying in Qom, the epicentre of the Iran outbreak, according to a Chinese student at the University of Qom who preferred to remain anonymous. The capital city, Tehran, is host to an even larger Chinese community that works in construction, catering, and other industries, including many students at the University of Tehran.

With the Iranian government's waiving of visa requirements in September 2019, a growing number of tourists have also been visiting: Between September and December last year, the number of Chinese tourists entering Iran rose by 130,000 compared with the same period in the previous year, according to Iran's official news agency, IRNA.

To try and avoid further spread of the virus and with the increased difficulty in tracking passengers' travel history posed by indirect flights, all Chinese citizens in Iran have been advised to fly directly back to China rather than transiting through another location.

Evacuation from Iran

A Chinese student who studies at the University of Tehran confirmed with Al Jazeera that the Chinese Embassy in Tehran had liaised with China Southern Airlines to evacuate Chinese citizens in Iran, two weeks after Iran reported its first COVID-19 case.

The first flight departed Tehran on the night of March 3 with seats for approximately 200 people. The student said that, according to the message sent by the Chinese embassy, priority was given to students who were stuck in Qom and that the flight would fly direct from Tehran to Lanzhou - a city in China's far west.

Previously, the embassy had advised Chinese citizens to refrain from travelling via a third country and to wait for the official charter flight, according to a statement shared with Al Jazeera by the student.

Yang, a Chinese student at the university, returned from Iran before the embassy issued the statement. In her apartment in Beijing, she recalled her trip home.

"We received the news of the first confirmed cases in Iran on February 19 and two deaths were reported that night already, so I immediately felt the situation was going to be tricky," Yang, requesting to be identified only by her surname, said from home while exercising a 14-day self-quarantine. "As more countries started to close their borders with Iran, I thought I needed to get out as soon as possible."

Similar to the route used by a Chinese citizen who returned from Iran and was later confirmed to be infected, Yang took a flight to Moscow and then on to Beijing on February 28 - a day before the first imported case was reported in China.

China has developed close ties in business and tourism with Iran and hundreds of Chinese study at Iranian universities [File: West Asia News Agency via Reuters]

"There were no confirmed cases on our flight, and no one was having any fever, so we went through the normal procedure and got our temperatures checked before being let back home," Yang recalled of the relatively smooth journey.

"Now I have a card attached to my front door that says: 'This household has a person(s) who has recently returned to Beijing and is exercising self-quarantine from February 28 to March 12.'"

Working in Italy

As of March 3, Qingtian county in Zhejiang province had reported a total of 8 imported cases from Italy - the highest in the country so far. More than 300,000 people from Qingtian county are known to have gone overseas to work, some 100,000 of them to Italy, which recorded the highest number of deaths after China.

So far, more than 100 people have returned to Qingtian from Italy but the local government has tried to persuade those still there to stay put.

"Those who return to Qingtian are not only running risk of getting infected or spreading virus on the way back to China, but also posing an additional challenge to the health of their family and our city," the government said in a notice.

The alert also laid out quarantine rules for those who are returning or already made their way home: All returning overseas Chinese should register with the government to clarify whether they have been to any virus-infected areas in the past 14 days, and everyone returning will also be put under a mandatory 14-day quarantine.

Such measures are being taken in other provinces and cities, too.

Travellers from South Korea, Japan, and Italy are also seen as a risk, as China's own outbreak - still the world's largest - appears to be coming under control.

75 passengers entering #China have been #positive in nucleic acid test, said China's General Administration of Customs, revealing the data for the first time on Wednesday, amid rising concerns over the #coronavirus spread worldwide. #COVID19 https://t.co/BR1irnvRzt pic.twitter.com/nU2N2SdkyJ — Global Times (@globaltimesnews) March 4, 2020

Qingdao, a coastal city in northeastern China that has close commercial ties with South Korea and Japan, received more than 20,000 travellers from overseas between January 24 and February 24.

The city government has categorised them into four groups for different levels of quarantine: people with travel history to infected countries; people who have come into close contact with confirmed patients while overseas; passengers who took the same flight with someone who has symptoms; and people who are found to have a fever at the border inspection.

'Only exit, no entry'

In Jilin, a northern Chinese province with close ties to South Korea, passengers travelling from areas with confirmed cases are asked to sign a declaration agreeing to a mandatory 14-day quarantine.

Provinces such as Zhejiang, Ningxia, and Guangdong are also adopting similar measures with a focus on citizens returning home.

Some border crossings have begun denying entry to foreigners.

"We are currently adopting the 'only exit, no entry' policy: Only people who wish to exit Shenzhen can leave, and no foreigner can enter," Li Shuntao, a border inspection official at Shenzhen's Shekou border crossing which has connections with Hong Kong and Macau, told Al Jazeera. "This policy had been in place since February 29."

By sealing off millions of people who live in Wuhan and the rest of Hubei province, China has already shown its willingness to take aggressive measures to curb the outbreak. Those who fail to comply with orders risk breaking civil and criminal laws, depending on the specific situation.

But, while some countries have blocked entry to Chinese and stopped flights and some of its own local governments appear to be doing the same, Beijing insists it will not seal itself off from the world.

"In the current international environment, there is no way we will practice prevention and control by 'closing up' China," Zhao Lijian. spokesman for the Ministry of Foreign Affairs said in a news conference on March 2.

"Only through global collaboration can we succeed in defeating the virus."