Hong Kong (CNN) — The coronavirus is “easily the most serious public health emergency” the World Health Organization (WHO) has faced, its director-general said on Monday, after countries that previously seemed to have the pandemic under control recorded a rebound In the cases.

Across the Asia-Pacific region, where countries were first affected by the virus and first to contain it, there have been new and, in some cases, apparently unexplained increases in the number of infections. Governments that had previously been praised for their response to the pandemic now appear to be struggling.

This is disturbing news for those where the first wave of the virus has yet to be fully controlled, let alone in the disaster areas of the United States and Brazil. It’s especially scary, as there are only a few more weeks of summer left in some parts of the northern hemisphere, and many epidemiologists expect the virus to grow again in winter.

LEE: China Offers $ 1 Billion Loan to Latin America and the Caribbean for Access to Covid-19 Vaccine

Setbacks in Asia-Pacific

On Tuesday, China reported the highest number of locally transmitted coronavirus cases since early March for the second consecutive day, with the majority of the 64 new domestic cases in Xinjiang. The far west region has seen a new outbreak in its capital Urumqi since July 15, after nearly five months without new cases.

In southern Hong Kong, the semi-autonomous Chinese city is also experiencing a major new outbreak, with more than a thousand new cases in the past two weeks and six days in a row with more than 100 cases. The new surge came after the city appeared to be nearly virus-free, easing restrictions and starting discussion of possible “travel bubbles” with other parts of the world after the pandemic.

While there was a slight decline in the number of cases recorded on Monday, Japan has seen some of its worst numbers since the early stages of the pandemic, with some 5,000 new cases in the past week, according to data from Johns Hopkins University (JHU ). The worst of the new outbreak has focused on the capital, Tokyo, which recorded six consecutive days of more than 200 new cases until Monday, when there were 131 cases. However, that drop may be due to far fewer tests being conducted during a planned four-day vacation weekend to promote domestic tourism.

Elsewhere in Asia-Pacific, Australia is also experiencing a large increase in the number of cases. The country had only a handful of cases in June, but that increased at the end of the month and exploded in July, with the most affected area, the southern state of Victoria, which announced another 384 cases on Monday. There are 4,775 active cases in Victoria, of which 414 are health workers, putting further pressure on the state’s ability to treat the sick.

LOOK: Late results, group testing and a threat that worries more than 40 million people in Latin America

What happened?

Many of the latest waves of the virus, in Hong Kong, Australia, China and elsewhere, have surprised officials. While there are a number of flaws to note in the responses from various governments, the figures did not explode until very recently, possibly because a more virulent strain was introduced, or because cases were simply piling up undetected and suddenly hitting a inflection point.

Ben Cowling, a professor at the University of Hong Kong’s School of Public Health, wrote this week that “we may never know” how the latest wave of cases started in the city, but the data suggests that infections are being imported from abroad. .

“When you control (this) epidemic, this really emphasizes the importance of keeping infections out through effective testing and quarantine of people arriving in Hong Kong,” he said. “Once an epidemic begins, it will take a lot of effort to stop it.”

Speaking on Monday, Hong Kong’s second-in-command, Matthew Cheung, said the city had followed the “lift and remove” approach, gradually relaxing the restrictions as cases decreased and raising them again if an increase occurred.

This week, the government announced that it would make the use of face masks mandatory in public, a rather redundant measure given that almost all Hong Kong people already did, and limiting public meetings to only two people. The Chinese government will also help build a makeshift Wuhan-style hospital near Hong Kong Airport with a capacity of around 2,000 beds.

“The epidemic situation is critical,” Cheung said, adding that the coming weeks are extremely crucial for the city. “We face a high risk of outbreak in the community.”

City officials have faced criticism for their handling of the latest wave, particularly over the plethora of quarantine waivers granted to business travelers and airline crews, who were blamed by some for reintroducing the virus into the city. However, the government has defended the policy as necessary for the economy, and health authorities have not yet been able to trace where the latest infections originated.

And despite all of Cheung’s insistence that Hong Kong has been pursuing a “lift and suppress” policy, the city would still have to possibly introduce full confinement, even as cases continue to escalate.

That’s not the case in Australia, where Victoria has been subjected to strict restrictions, but is struggling to get the numbers back under control. Speaking to ABC, the country’s public broadcaster, experts advised patience, saying the confinement is likely working, but that many infections occurred weeks ago and are barely being detected.

The most extreme action in the region occurred in Vietnam, where the government began evacuating some 80,000 tourists from the central city of Da Nang on Monday after three residents contracted the virus.

Vietnam has emerged as an example in virus containment, thanks to an aggressive early-detection strategy for passengers at airports and a strict quarantine and monitoring program. The country has not reported any deaths from covid-19 and has confirmed only 431 cases, according to Johns Hopkins University.

OPINION | Why might the next 100 days be the most important in American history?

Difficult task ahead

The difficulty that even the Asia-Pacific countries, the region of the world with perhaps the best coronavirus response, are having makes the task of controlling the virus in other parts of the world potentially unattainable, at least until a vaccine is available.

Even with the new increases, the numbers in Australia, Hong Kong, and Japan are not close to what is happening in the United States and Brazil, which are still dealing with the first wave of the pandemic and have yet to take concerted action at the national level. that experts have long recommended.

LEE: United States Registers More Than 1,000 Coronavirus Deaths Over Four Days In A Row As Experts Urge Country To Close

And while the July heat may make the northern hemisphere winter seem far away, it is getting closer. Scientists say countries must prepare for a possible rebound in cases that could be more serious than the initial outbreak, as cold weather pushes people into poorly ventilated spaces, exactly the conditions that are likely to cause the new coronavirus to spread more easily.

More than ever, hope lies in the dozens of vaccines against the developing coronavirus. Speaking Monday, Dr. Anthony Fauci, an expert in infectious diseases in the United States, said that if one is effective and enough people take it, that could end this pandemic.

“If we get a widespread vaccine, we can end this pandemic and create a veil of immunity in this country, preventing the infection from coming back,” he said.

CNN’s Julia Hollingsworth, Katie Hunt and Eric Cheung contributed to the reports.

.