Cases of nCoV of unknown origin pose a challenge to national governments because they do not know where and how to deal with them.

While Asia-Pacific is struggling to cope with a rising wave of nCoV infections, the emergence of unidentified and unknown cases of transmission is causing anxiety among governments.

An increasing number of such cases force governments, such as Australia or Hong Kong, to take drastic and broader measures, bringing the entire city back to a state of blockade.

"You can hardly stop the virus from spreading because you don't know where it will break out next," said Yang Conganan, former deputy general manager of the China Centers for Disease Control and Prevention.

On the contrary, in places where the number of unexplained cases is low, such as South Korea or Japan, the government can somewhat relax even though the total number of new cases per day is up to hundreds.

The number of unexplained cases will be an indication of where there is a high possibility of re-outbreak and where people need to be prepared to face the re-blockade order.

Hong Kong spent three relatively peaceful months before a serious infection broke out earlier this month.

Hong Kong responded very quickly, re-imposing the most stringent measures on 7.5 million people.

In Japan, officials use the term "unidentified case of infection" to refer to unidentified cases of nCoV infection.

But the number of unexplained cases is rising to about 45%, ringing the alarm.

On July 15, Tokyo raised the alert to the highest level on a four-level scale, advising people to be vigilant in their behavior to prevent the virus from spreading.

"We need to ensure that this wave does not spread and cause the government to declare a state of emergency," Minister Nishimura said on July 14.

South Korea has been praised for its success in disease control efforts through rapid and aggressive testing to trace the source of infection, helping them not to apply blockade measures and remain calm before the possibility of epidemic.

This is due to the fact that only one fifth of all new infections in Korea in the first two weeks of July are those of unknown origin.

Although the government has adopted access control systems in high-risk areas such as gyms or nightclubs, South Korea still doesn't need to use more restrictive measures to limit the movement of

"Korea has very few inexplicable hotspots," Yang said.

In Australia, 5 million people in Melbourne are living under a six-week mandatory blockade due to a new nCoV outbreak in Victoria.