Brazilian President Jair Bolsonaro, who has consistently downplayed the risks of coronavirus, announced Tuesday he has tested positive, as the United States -- the nation hardest hit by the pandemic -- formally launched its withdrawal from the World Health Organization (WHO).

The UN health agency meanwhile acknowledged that there was "emerging evidence" of airborne transmission of COVID-19, which has infected nearly 11.7 million people around the globe and caused more than 539,000 deaths.

Bolsonaro, who said he had experienced only mild symptoms, has ignored containment measures such as social distancing, despite Brazil being the second-worst hit country, with more than 66,000 dead.

The far-right leader, who at 65 is in the highest-risk age category, insisted he was feeling "perfectly well" and took off his face mask during a TV interview announcing his test results.

He repeated his mantra that the "collateral effects" of the virus should not be worse than the illness itself.

Since the beginning of the virus outbreak, Bolsonaro has minimized the risks of what he initially called "a little flu" while resisting wearing a mask in public.

Brazil is a large reason why Latin America and the Caribbean has now surpassed three million cases, according to an AFP tally. 

The region has seen nearly 140,000 deaths, nearly half of them in Brazil.

- 'Chaotic and incoherent' -
In Washington, a senior US official said the United States had informed UN Secretary General Antonio Guterres of its intention to leave the WHO, effective July 6, 2021.

President Donald Trump has been critical of the WHO's pandemic response, accusing it of bias toward China and ignoring early signs of human-to-human transmission of the deadly virus.

The United States is the largest financial contributor to the WHO -- which leads the fight on global maladies from polio and measles to mental health -- providing $400 million annually.

Joe Biden, the presumptive Democratic presidential nominee, said Tuesday he would immediately reverse the decision and keep the US in the WHO if he defeats Trump in November.

Senator Robert Menendez, the top Democrat on the Foreign Relations Committee, criticized the Trump administration's move.

"To call Trump's response to COVID chaotic and incoherent doesn't do it justice," Menendez said. 

"This won't protect American lives or interests -- it leaves Americans sick & America alone."

- 'Unsustainably high numbers' -
Critics say Trump is seeking to deflect criticism from his own handling of the pandemic, which has killed nearly 131,000 people in the United States, by far the highest death toll of any nation.

Officials have said hospitals in some parts of the country are in danger of being overwhelmed, with many states hit particularly hard after they eased virus restrictions.

Texas -- one of the new US hotspots -- on Tuesday registered a new daily case total of 10,028, making it the third state after New York and Florida to hit the grim milestone.

Top infectious disease expert Anthony Fauci has warned the country is still "knee-deep" in the first coronavirus wave.

But Trump pounced on that comment Tuesday, saying the United States was "in a good place" and adding: "I disagree with him."

Experts are still struggling to understand COVID-19, and the WHO said it was open to new research after scientists lobbied for it to stress that the virus can spread through the air farther and for longer than initially believed. 

There have been explosions of infections across the world, including Iran, which announced 200 new deaths on Tuesday.

Australia on Tuesday ordered five million people locked down in Melbourne, its second-biggest city, to combat a surge in cases.

"We can't pretend" the crisis is over, said Daniel Andrews, premier of Victoria state.

The restrictions in the Melbourne area will last at least six weeks, while Victoria state will be effectively sealed off from the rest of the country.

Cases are also surging in India and four new coronavirus field hospitals were opened on Tuesday in the financial capital Mumbai as the nationwide death toll jumped past 20,000.

- 'Viral bomb' -
Italy's health minister ordered a one-week suspension of flights to Rome from Bangladesh on Tuesday, after 21 passengers arriving from Dhaka tested positive, adding to the number of cases within the Bangladeshi community in the Lazio region surrounding Rome. 

Lazio's top health official Alessio D'Amato called it a "veritable viral 'bomb' that we've defused."

Meanwhile, the head of the prestigious Royal Society science journal said Tuesday that people who refuse to wear face masks during the pandemic should be stigmatized in the same manner as drink-drivers.

"If all of us wear one, we protect each other and thereby ourselves, reducing transmission," wrote Venki Ramakrishnan.

Panic returns to Melbourne

Shoppers in Australia's second-biggest city stripped supermarket shelves Wednesday as millions in Melbourne prepared for a return to virus lockdown, with warnings the new restrictions will cost the economy Aus$1 billion a week.

Five million residents were ordered back into a six-week lockdown beginning midnight Wednesday into Thursday as soaring community transmission of the coronavirus brings more than 100 new cases daily.

A further 134 infections were detected in the past 24 hours -- small in comparison to the tens of thousands in hard-hit countries like the US and Brazil but considered a major spike in Australia, which had otherwise been successful in containing COVID-19.

The country's largest supermarket chain, Woolworths, said it had reimposed buying limits on items including pasta, vegetables and sugar after shoppers rushed to stores across Victoria state.

Experts have warned that people everywhere will have to get used to the "new normal" of on-and-off restrictions as new clusters emerge and subside, while there are also concerns over the economic and health impacts the measures will bring.

Treasurer Josh Frydenberg said the Melbourne lockdown would cost the economy up to Aus$1 billion ($700 million) a week, telling public broadcaster ABC the burden would "fall heavily on businesses".

Restaurants and cafes will be limited to serving takeaway food, while gyms, beauty salons and cinemas will be forced to close again.

Residents will be restricted to their homes except for work, exercise, medical care or to buy essentials -- a return to social isolation that was only recently lifted.

Professor Michael Kyrios, a clinical psychologist at Flinders University, warned that Victoria needed to brace for a "coming mental health crisis" as a result.

"This will likely place the mental health care system in a precarious situation with very limited ability to mobilise resources in response to the increased incidence of mental illness arising from the COVID crisis," he said.

State Premier Daniel Andrews on Wednesday acknowledged the costs to Victoria's 6.6 million residents, saying his job required him "to make not just the popular calls, but the really difficult, the hard calls".

"This is not the situation that anybody wanted to be in but it is the reality that we must confront," he said.

"To do otherwise is to pretend that this isn't real, to pretend that we have other options."

Health authorities say they have linked many of the Melbourne cases to hotels where residents returning from overseas were being quarantined.

Local media reported security guards had breached infection control protocols -- including allegedly having sex with guests being held in isolation -- prompting the government to replace the private contractors with prison staff and launch an inquiry.

But there is also concern over the increased community transmission in Melbourne, with just 11 of Wednesday's new cases linked to known outbreaks.

Around 3,000 people in the city have already been locked inside their homes since Saturday in Australia's strictest coronavirus response to date after a cluster emerged in a high-rise public housing estate.

A total of 75 cases have been detected in the densely populated towers during a major testing blitz.

Long queues of cars were backed up at Victoria's border Wednesday after neighbouring New South Wales closed the boundary for the first time in the pandemic -- essentially sealing off the state from the rest of Australia.

The hastily announced decision left residents of border towns scrambling to obtain permits to cross for work or other essential reasons, while school holiday travellers were rushing to return home.

Australia has recorded almost 9,000 cases of COVID-19 and 106 deaths from the virus.

'Second wave' batters Central Asia

At a call centre functioning as a coronavirus hotline in Kyrgyzstan's capital Bishkek, the volunteers manning the telephones are under siege.

Call centre coordinator Askhat Abdykerimov says he and his team of more than 60 medics and medical students are now fielding at least 3,000 calls per week.

"When the call centre first opened, we had plenty of calls of a non-medical nature," Abdykerimov told AFP.

"Now nearly all calls are people ringing in with symptoms of coronavirus infections."

Bishkek has become a new regional epicentre of the disease that has re-emerged with a vengeance since Kyrgyzstan and fellow ex-Soviet neighbours Kazakhstan and Uzbekistan began relaxing stay-at-home restrictions in May.

Even Turkmenistan, which still insists it is virus-free, on Monday welcomed a 10-day WHO mission that will examine the secretive country's response to the pandemic.

In Kyrgyzstan, registered daily infections have twice topped 500 this month -- more than the total number of people recorded as ill with coronavirus at the time the lockdown was relaxed in late May.

The country has reported more than 8,000 cases but many say the real number of infections is higher, pointing to overflowing hospitals and social media timelines thick with condolences and cries for assistance.

A lack of tests, as well as their poor quality, are two reasons coronavirus is increasingly not being diagnosed or counted as a cause of death, experts say.

Aigul Sarykbayeva, a 54-year-old queuing for a drip treatment at the capital's main indoor sports venue -- recently repurposed as a hospital -- has not yet been able to get tested for the virus.

But after battling to secure a lung scan, Sarykbayeva was diagnosed with pneumonia -- a condition caused by the virus that she said is ripping through her neighbourhood. 

"I sometimes think to myself, is there anyone I know who isn't ill? Absolutely everyone is ill," she told AFP.

- Firework fury - 

Kazakhstan, the richest of the five Central Asian states, has also seen its hospitals overwhelmed and drug supplies squeezed as registered cases have grown four-fold since the beginning of last month to top 48,000.  

Yevgeny Yeremin, a man who was in a long queue to buy medicines in the former capital Almaty, said he had considered coronavirus a "joke" and "something political" before his grandfather died from the virus and his elderly mother grew seriously ill.

Complaints poured onto social media on Monday after officials marked a public holiday honouring the capital Nur-Sultan -- named in honour of ex-leader Nursultan Nazarbayev -- with an ostentatious firework display in the city.

Dimash Kudaibergen, a singer with a massive following in China as well as his homeland, was among those who criticised the move that came as the official virus death toll reached 264 people.

"Fireworks in honour of what?" the star wrote on his Instagram page with 3.3 million followers. "In honour of taking the first place for coronavirus cases?" 

- Bottlenecks -

While Kazakhstan has this month reintroduced some of the restrictions that it first imposed in March, officials in Kyrgyzstan have said they are not considering a second lockdown.

The government has admitted that pandemic-related aid received from international donors was used to pay state salaries and plug budget holes compounded by lockdown, rather than strengthen the health system.

Across the corruption-prone region, the surge in cases has helped fuel accusations that officials are embezzling donor money.