(CNN) — China is stepping up measures to prevent coronavirus cases being imported back from other virus-hit nations, as the outbreak slows within the country but picks up speed across the world.

The deadly virus has spread to more than 75 countries and territories worldwide since emerging from China late last year. The number of new daily cases reported outside China has now far exceeded the number of infections announced each day within the country.

Despite the decline of new cases, Chinese authorities are on high alert following an uptick of imported cases from overseas since last week.

Multiple cities and provinces -- including Beijing, Shanghai and Guangdong -- have announced a 14-day quarantine for people arriving from overseas, with the strictest restrictions placed on those coming from countries with severe outbreaks, such as Italy, Iran, South Korea and Japan.

China's effort to prevent imported cases comes amid rising nationalist pride that the country's sweeping measures to contain the outbreak -- and the self-sacrifice of the Chinese people -- offered other nations a crucial window to prepare for its spread. There is also growing criticism online against other governments for their allegedly slow response to control the outbreak. Both sentiments have been played up in state media.

Imported cases

So far, China has confirmed 20 imported cases, mostly expatriate Chinese who returned to their hometowns as the outbreak flared up in their host countries.

By the end of Tuesday, 6,728 overseas passengers had arrived in China showing symptoms of infection, according to the General Administration of Customs. Among them 779 were suspected coronavirus cases and 75 showed positive results from initial nucleic acid tests, the administration said in a statement on its website.

Some local governments in China have urged overseas Chinese to reconsider their homecoming plans for the sake of their "family's health and safety."

Zhejiang, an affluent province on the country's east coast with a large number of emigrants, reported seven new imported cases Tuesday.

According to local authorities, all of them are Chinese nationals returning from Italy, which is facing the biggest outbreak in Europe with 3,089 confirmed cases and 107 deaths as of Thursday.

The seven people, who worked and lived in the northern Italian town of Bergamo, returned to their hometown of Qingtian county via Shanghai last week. They tested positive for the coronavirus on Monday, according to the Qingtian government.

None of them had been to Hubei province or its capital Wuhan, where the outbreak first emerged, the government said.

The seven returnees all had close contact with a woman confirmed to have the virus on Sunday. The woman, surnamed Wang, was the first imported case of Zhejiang province. The eight worked together at the same restaurant in Bergamo, an hour's drive from Milan, the Qingtian government said in a statement on its social media account.

According to the Qingtian government, Wang began coughing on February 16. She boarded a flight in Milan on February 26 and landed in Shanghai via Moscow. Six of the imported cases took the same flight as her, and the other one left Italy two days later via Germany.

"What we're trying to isolate is the virus, but what cannot be severed are the bonds of flesh and blood between overseas Chinese and their families in their hometowns," the Qingtian government said.

"For the sake of your family's health and safety, please strengthen your precautions and prudently decide on your travel plans to minimize mobility," it added.

Qingtian, named after its green rice paddies, is known for its large number of overseas immigrants. Around 300,000 people from the county live overseas, including 100,000 in Italy, according to the state-run Xinhua news agency.

On Thursday, Zhejiang provincial health authorities reported another two imported cases in the city of Huzhou, both returnees from Italy.

Self-quarantine for overseas travelers

When the outbreak started to flare in late January, the Chinese government was critical of countries -- especially the United States -- for placing travel restrictions on China.

From late January to early February, the Chinese foreign ministry repeatedly lashed out at the US for its response to the outbreak, accusing it of "going in the opposite way" of the World Health Organization's advice against travel restrictions on China, saying it was "certainly not a gesture of goodwill."

As the outbreak spiraled into a full public health crisis, an increasing number of countries and regions moved to shun Chinese visitors.

But the tables seem to be turning. As the number of new infected cases shoot up abroad, the increase of confirmed cases in China has slowed steadily -- a development that spurred some Chinese nationalists into pride and indignation.

"Now, we should rightfully declare that the US owes China an apology, the world owes China a thank you," reads a social media article carried on Xinhua's website, which criticized the US for its slow response to contain the virus within its own borders.

So far, China has not imposed travel restrictions on these countries, despite the rapidly worsening situations in Iran, Italy and South Korea. But multiple local authorities have dialed up quarantine efforts for overseas arrivals.

The financial hub of Shanghai, where the eight Qingtian returnees landed, announced Tuesday that it will require all people, regardless of nationality, to go into quarantine for 14 days if they have arrived from a "key country or region" with serious outbreak conditions.

Similar measures have also been adopted in Beijing, the southern province of Guangdong and the cities of Qingdao and Weihai in eastern Shandong province.

Shandong is just an hour's flight from South Korea, which has the most confirmed cases outside China. As of Wednesday, South Korea reported 5,766 confirmed cases and 35 deaths.

Last week, Zhong Nanshan, a government-appointed respiratory expert, already warned at a press conference in Guangzhou that with the rapid spread of the virus abroad, China could "go from exporting infected cases to importing cases."

He was soon proved right.

On Saturday, Beijing reported two imported cases who had returned from Iran, another badly hit country where 92 people have been killed by the virus, including an adviser to Iranian Supreme Leader Ayatollah Ali Khamenei and one of the country's top clerics.

Both cases had close contact with a translator who returned from Iran to the Ningxia Hui Autonomous Region in northwest China. The 23-year-old man was confirmed to have the virus on February 26, according to local authorities, and is believed to be the first imported case reported.

'We're under huge pressure'

In Beijing, the municipal government announced at a pres conference Wednesday that anyone arriving in the capital from South Korea, Italy, Iran and Japan must undergo a 14-day quarantine at home or at a designated hotel.

Chen Bei, a municipal government official, said some overseas Chinese students and workers were eager to return home as the outbreak spreads quickly in other countries. "In recent days, more than 20 Chinese students have returned from Iran via Beijing," she was quoted by Xinhua as saying.

"As one of the most important port of entries in the country, we're under huge pressure to prevent the outbreak from being imported (back in China)," she added.

Since February 14, Beijing had ordered everyone who returned to the capital to go into self-quarantine for two weeks. The rules were slightly loosened a week later, exempting overseas travelers and some other groups from self-quarantine.

But some residential communities have already been carrying out quarantines for residents returning from virus-hit countries before the announcement on Tuesday.

Bill Birtles, a Beijing-based correspondent for the Australian Broadcasting Corporation, was visited by a building manager after he returned from South Korea for a reporting trip last week. A notice was later affixed to the outside of his apartment door.

The notice, written in Chinese, informs his neighbors that the occupant of this apartment has recently returned from South Korea and is now in self-quarantine.

"For everyone's physical and psychological health, me and my family are now staying home for medical observation until March 10," the notice reads. "Thank you for your understanding and support."

Birtles told CNN that he also been required to sign a statement agreeing to the quarantine, and report his daily temperature readings in a WeChat group set up by the property management company for the about a dozen residents quarantined at home in the building.

"The lesson is -- short assignments out of Beijing aren't worth the 14 days home (isolation) when you get back," he wrote on Twitter.

This story was first published on CNN.com, "China is trying to prevent coronavirus from being brought back from other countries"