Bolivia's interim president became the latest world leader to test positive for the coronavirus Thursday, as the United States notched yet another record-breaking surge of cases while global infections and fatalities continued their relentless rise.

COVID-19 has now claimed more than 550,000 lives across the planet, and infected more than 12 million people since it first emerged in China in late 2019 -- among them Brazilian President Jair Bolsonaro, British Prime Minister Boris Johnson and now Bolivia's Jeanine Anez.

In a video on Twitter Anez said she was "fine" and would continue working from isolation. Bolsonaro said he was feeling "very well" on Thursday after announcing he had the virus earlier this week, and Johnson, who contracted the respiratory disease in March, has recovered.

Bolivia is gearing up for a general election, despite the country of 11 million recording almost 43,000 virus infections and more than 1,500 deaths.

By the time the polls are held in less than two months, the government expects there to be 130,000 cases.

The United States notched up half that figure in just one day Thursday, with 65,551 new cases recorded by Baltimore-based Johns Hopkins University -- a new high.

The country, the hardest-hit in the world by the pandemic, has a total caseload of more than 3.1 million, with 133,195 deaths.

It has seen a spike in infections in recent weeks, and health experts worry the death rate may soon follow the same trajectory.

"We're in a very difficult, challenging period right now," top US infectious diseases expert Anthony Fauci said.

"I would think we need to get the states pausing in their opening process," he said, although he added: "I don't think we need to go back to an extreme of shutting down."

US President Donald Trump, who has publicly disagreed with Fauci, has downplayed the spike.

"For the 1/100th time, the reason we show so many Cases, compared to other countries that haven't done nearly as well as we have, is that our TESTING is much bigger and better," he tweeted.

"We have tested 40,000,000 people. If we did 20,000,000 instead, Cases would be half, etc."

- 'We're totally exhausted' -
The virus is still infecting new populations: the first case was recorded in northwest Syria on Thursday, reviving fears of disaster if the pandemic reaches the rebel bastion's displacement camps.

And the response remains chaotic in places already in the grip of outbreaks.

Exhausted medics in Algeria pleaded for authorities to enforce hygiene rules.

"We're working non-stop. We're totally exhausted," said Dr Mohamed Yousfi, head of infectiology at the Boufarik hospital near Algiers. 

Some staff are so tired they have fainted or had car accidents, he said.

Meanwhile thousands of angry Serbians protested for a third day against the government's handling of the crisis -- though the demonstrations remained largely peaceful after two nights of violence.

Fear and anxiety remains high for many. In South Africa, where the outbreak is yet to peak, authorities rushed to calm citizens after health officials said they were ready to bury more than a million people, with long rows of graves already dug.

And, in a potentially worrying discovery, scientists in Italy said there was "strong evidence" that COVID-19 positive mothers can pass the virus on to their unborn children.

Virus lockdowns have dealt a staggering blow to the global economy, and the outlook remained bleak Thursday.

The pandemic could push 45 million people from the middle classes into poverty in already economically troubled Latin America and the Caribbean, the United Nations warned.

European and US stocks finished mostly lower amid lingering virus worries. Another 1.3 million US workers filed for unemployment last week, government figures showed -- though the pace of layoffs has slowed.

- 'Virus thrives on division' -
As talk of a second wave of the virus multiplies, some of the world's most populous nations including India, Pakistan and Brazil are still reeling from their first outbreaks.

In the Middle East, hard-hit Iran reported a record single-day death toll of 221, taking its total over 12,300.

In Europe, France continued to re-emerge from the darkest days, announcing the Eiffel Tower would reopen its top level for the first time in three months. Gyms and pools are set to reopen in England later this month. 

However countries farther east have found themselves plunged back into restrictions with a resurgent virus, such as Bulgaria, which banned sports fans from stadiums and shut bars and clubs.

Meanwhile the World Health Organization, under fire from Trump over its handling of the pandemic, opened an inquiry into its response Thursday, with initial findings due next year.

"The virus thrives on division but is thwarted when we unite," said WHO chief Tedros Adhanom Ghebreyesus, pleading for togetherness.

Australia cuts citizen returns

Australia will slash the number of returning citizens allowed into the country by half as it struggles to contain an outbreak of coronavirus in its second-largest city, officials announced Friday.

From Monday, only 4,000 Australian citizens or permanent residents will be allowed back into the country each day, down from around 8,000 currently, Prime Minister Scott Morrison said.

The announcement came as officials in the state of Victoria reported a record 288 new COVID-19 cases mainly in the state capital, Melbourne.

Some five million residents of greater Melbourne were ordered into a six-week lockdown this week in an effort to curb the outbreak, which has rattled a nation that had successfully contained the epidemic in most areas weeks ago.

Health authorities said it would take several weeks to know if the Melbourne lockdown has succeeded in stemming the surge.

Australia closed its international borders to all but returning citizens and permanent residents in late March as coronavirus mounted.

All returning travellers have been put in mandatory hotel quarantine, stretching resources in the country's main cities. 

Morrison said the cap on returning Australians would remain in place until the Melbourne epidemic is contained.

Health and security breaches in quarantine hotels in Melbourne have been blamed for sparking the outbreak there, and nationwide returning overseas travellers have accounted for the majority of COVID-19 cases in Australia.

Bolsonaro feels 'very well', praises hydroxycholoroquine

Brazilian President Jair Bolsonaro, who has tested positive for COVID-19, said on Facebook Thursday that he was "very well" and again advocated the use of the controversial drug hydroxychloroquine. 

Bolsonaro, 65, appeared in his weekly Facebook Live post at his official residence. He appeared to be in good shape and was not accompanied, as is often the case, by ministers or senior officials, and the usual sign language interpreter was not present.

Since the beginning of the crisis, the far-right president has dismissed the seriousness of the epidemic and criticized containment measures ordered by governors in Brazilian states. 

Bolsonaro said that after feeling unwell at the end of last week, he had started taking one hydroxychloroquine tablet every day. 

The drug, originally tested to fight malaria, has been pushed as a treatment for COVID-19 in many countries -- but its effectiveness has not been formally proven and the issue is deeply dividing the global scientific community. 

"I'm saying this very clearly," Bolsonaro said in his video. 

"I took (hydroxychloroquine) and it worked, and I'm fine, thank God. And let those who criticize it at least offer an alternative." 

He did, however, deny making "propaganda for hydroxychloroquine". 

Brazil is currently the second country hardest-hit country in the world by the pandemic, behind the United States.

The death toll on Thursday was 69,184, with an increase of 1,224 in the previous 24 hours.

Mexico reports new record virus cases

Mexico on Thursday posted 7,280 new coronavirus cases in 24 hours, a daily record, and an additional 730 deaths, data from the health ministry showed.

According to the ministry's daily update, the Latin American country has recorded 282,283 infections and 33,526 deaths since its first case was reported in late February.

"The risk of infection remains high, and it is therefore necessary to apply health measures to prevent an increase in cases," Jose Luis Alomia, national director of the Department of Epidemiology of the Ministry of Health, said during his daily press conference.

Despite Thursday's record, Alomia said that positive cases and deaths were trending downward overall throughout the country.

Mexico began gradually reopening its economy in June, a decision that -- according to Hugo Lopez Gatell, the deputy health minister in charge of the fight against the pandemic -- still carries a risk of an increase in cases.

The country of 127 million is the fifth-hardest hit country in terms of death toll, after the United States, Brazil, the United Kingdom and Italy.

Italy bans entry from 13 nations

Italy on Thursday banned travellers from Brazil and 12 other countries it considers to pose a high risk of COVID-19 transmission.

The full list comprises Armenia, Bahrain, Bangladesh, Bosnia, Brazil, Chile, the Dominican Republic, Kuwait, North Macedonia, Moldova, Oman, Panama and Peru.

The decree banning visitors from those countries from entering Italy was signed by the health ministry in agreement with the foreign, interior and transport ministries.

"Throughout the world, the pandemic has entered a more acute phase," said Health Minister Roberto Speranza.

"We cannot throw away the sacrifices made by Italians in recent months," he added.

Italy was the first country to be hit by the virus after it emerged in China late last year.

Almost 35,000 people have died of the virus in Italy, according to official figures, from more than 242,000 cases.