London CNN  — 

They were looked upon as examples of how to deal with the coronavirus, hailed for their no-nonsense approach, their clear messaging, their slick test-and-trace regimes, and the resulting low infection and death rates.

But now even countries celebrated for their handling of the pandemic are seeing a resurgence in Covid-19 cases. Take Australia: Five million people in its second-largest city, Melbourne, are contending with some of the harshest restrictions ever imposed there after authorities declared a “state of disaster” on Sunday.

The renewed outbreaks serve as a stark warning to global leaders of how quickly an apparent success story can unravel.

Australia

Just a few months ago, Australia was being lauded for its pandemic response.

Like the US, it closed its borders to foreign visitors who had recently been in China. As the virus spread, the government on March 19 closed its borders to all non-citizens and non-residents. Stricter curbs on social gatherings, expanded testing, and restaurant and bar closures followed as cases rose, with some states sealing their borders.

For a while, the outbreak was considered broadly under control.

Medical staff wearing PPE walk into the Flemington public housing flats on July 5 in Melbourne, Australia after nine public housing estates were locked down.

On May 8, Australian Prime Minister Scott Morrison announced plans to reopen the country by July, as the government began winding down social distancing measures. At the time, Australia’s case count stood at almost 7,000, with 97 fatalities.

But Covid-19 cases in the state of Victoria have spiked in recent weeks. The state recorded 671 new cases in a single day on Saturday, prompting state premier Daniel Andrews to declare a “state of disaster” on Sunday.

Thirteen new deaths were announced on Monday, bringing Victoria’s total to 136, and a total of 11,937 confirmed infections, according to the state’s chief health officer, Professor Brett Sutton.

The border between Victoria and New South Wales – Australia’s two most populous states – was closed for the first time in 100 years in July.

Lockdown measures in Melbourne have been bolstered further, with a curfew across the city for the next six weeks, non-essential industries shuttered, and schools returning to online classes.

Only one person is allowed to leave each home once a day – outside of curfew hours – to pick up essential goods, and they must stay within a 5 kilometer (3.1 miles) radius of their home.

As of Monday. Australia had reported more than 18,000 cases of Covid-19 with 221 fatalities.

Australia was once a success story, but now the border between New South Wales and Victoria has been closed after cases spiked in the latter state.

Hong Kong

Hong Kong was praised for its rapid response back in January, when it introduced measures including virus mapping and social distancing while encouraging hand-washing and other protective steps.

The government took further action to curb a second wave in March when Hong Kong residents began returning to the city, bringing the virus back with them. Authorities barred non-residents from entering Hong Kong, halted transit through the city’s airport, and implemented strict quarantine and testing on arrivals.

For many weeks, daily virus cases were down to single digits, and sometimes zero.

But despite these measures, Hong Kong has seen more than 1,000 new cases in recent weeks, and health officials have warned of a potential crisis if the outbreaks are not brought under control.

Public gatherings have been capped at two people, gyms have been closed and incoming travelers must now show evidence of a negative Covid-19 test. At the end of July, the city introduced a mask mandate for the first time, although many of its citizens had been wearing them anyway.

The city reported 80 new cases and two deaths on Monday – the first time in nearly two weeks that cases have dropped below triple digits – bringing the city’s total to 3,590 cases and 37 deaths.

Hong Kong’s Asia World-Expo center has been turned into a makeshift hospital with 500 beds; it began receiving coronavirus patients on Saturday afternoon, according to the Hong Kong government.

Germany

Europe’s poster child for how to handle a pandemic has hit rough waters in recent weeks.

Back in March, when more than 4% of patients with coronavirus were dying worldwide, Germany’s Covid-19 mortality rate stood at just 0.4%.

Over the months that followed, the country appeared to thwart the outbreak, thanks to its rapid response, mass testing and Chancellor Angela Merkel’s calm, clear communication of what was at stake.

Merkel announced plans to begin gradually re-opening the country. But new outbreaks soon followed the easing of the lockdown, with a spike of 900 cases in a day in May and a series of clusters recorded at slaughterhouses.

In June, the state of North-Rhine Westphalia imposed a new lockdown around a meat processing factory after more than a thousand workers there tested positive.

Authorities recorded 955 new cases last Friday, the highest figure since the beginning of May, according to its center for disease control, the Robert Koch Institute.

Germany’s Economy Minister Peter Altmaier called the figure “alarming” in a Twitter post, “especially since it is not large ‘hot spots,’ but smaller clusters of infections. The main risks need to clearly be named so that a more targeted prevention becomes possible,” he added.

The latest uptick has been attributed to laxer enforcement of distancing and hygiene rules, as well as travelers returning from abroad, prompting the health ministry to offer free coronavirus tests to travelers coming into the country. Tests will be mandatory for those returning from high-risk countries.

Vietnam

The country of 97 million lifted social distancing rules in April after a three-week national lockdown.

Vietnam’s initial success at containing the virus was thanks to an aggressive strategy of early screening of passengers at airports along with a strict quarantine and monitoring program.

It began to prepare for the outbreak weeks before its first case was detected, and after confirming the first few coronavirus cases, authorities were quick to take proactive measures – implementing the first large-scale lockdown outside China in February.

Tens of thousands of people were evacuated from Da Nang

Yet after nearly 100 days with no cases, last month Vietnam saw its largest single-day increase in infections since the pandemic hit the country in late January.

Three residents caught the virus in the central city of Da Nang, prompting the government to evacuate some 80,000 tourists in the area, suspend domestic flights to the city, and reimpose social distancing measures.

Infections have continued to spike and last week the country reported its first coronavirus fatality. Vietnam now has 642 confirmed cases and six deaths, according to Johns Hopkins University data.

As of Monday, a total of 103,268 people who have had close contact with patients or came from pandemic-hit areas have been placed under quarantine, according to the state-run Vietnam News Agency.

Japan

Japan also seemed to have responded effectively to the coronavirus without the sort of lockdown measures seen around the world.

On May 25, Prime Minister Shinzo Abe lifted the country’s state of emergency, saying in a briefing that “we were able to end the outbreak in about one month and a half with Japan’s own way.” He said the nation would gradually increase social and economic activities to create a “new life” with the coronavirus.

Parents and children enter a swimming pool open to a limited number of visitors as a preventive measure against coronavirus at Tokyo's Toshimaen amusement park on July 13.

But the country now faces a resurgence of the virus, recording some of its worst numbers since the pandemic began.

On Sunday, Japan recorded 1,331 new coronavirus cases – the fifth day in a row the country had recorded daily increase of over 1,000 infections, pushing the country’s total to 39,399 cases and 1,025 deaths.

New research from Japan suggests that many coronavirus clusters outside of hospitals may have been started by people who are younger than 40 or don’t feel sick, underscoring the importance of measures, such as face coverings, to slow the spread.

CNN’s Vanessa Yung, Isaac Yee, Angus Watson, James Griffiths, Helen Regan, Fred Pleitgen, Sol Han, Yoko Wakatsuki, Junko Ogura, Kaori Enjoji, Tomas Etzler, Ivana Kottasova and Oren Liebermann contributed reporting.