The United States topped three million confirmed coronavirus cases Wednesday as President Donald Trump pushed for schools to re-open amid a COVID-19 resurgence in many southern hotspots.

The US remains by far the worst affected country, with over 132,000 deaths, while Brazil -- whose virus-skeptic President Jair Bolsonaro has tested positive for the disease -- is a distant second with close to 67,000 deaths from almost 1.7 million cases.

As infections rose by a further 55,000 to reach a total of 3,046,351 on Wednesday, Trump called for students to return to their schools in the fall and lashed the Centers for Disease Control and Prevention for issuing guidance that he said was too restrictive.

The agency's head later said the guidelines were "not requirements" and that the CDC would soon update its advice.

Prestigious universities Harvard and MIT meanwhile sued the administration after it threatened to revoke the visas of foreign students whose entire courses have moved online because of the coronavirus pandemic.

- Chaos in Belgrade -

The virus has infected almost 12 million people worldwide and killed more than 500,000 since it emerged in China late last year.

Across the world, citizens chafed under renewed restrictions as countries experience fresh waves of disease. 

The Serbian capital Belgrade was hit by clashes for a second night as police skirmished with protesters outraged over the government's handling of the pandemic.

Clouds of tear gas and smoke filled the city center in chaotic scenes that mirrored violence the night before, when thousands came out to protest the return of a round-the-clock weekend lockdown.

In the Australian city of Melbourne, millions were preparing for a return to lockdown to fight an upsurge that is seeing more than 100 new cases reported each day, with panic buyers stripping supermarket shelves.

France, which had flattened its curve by imposing a strict lockdown earlier in the pandemic, said Wednesday it was girding for a possible surge in cases.

But, mindful of potentially disastrous consequences of attempting to thrust millions back into their homes, France's new prime minister aimed to soothe fears by promising no new full shutdown.

"We're not going to impose a lockdown like the one we did last March, because we've learned... that the economic and human consequences from a total lockdown are disastrous," Jean Castex said, promising "targeted" measures instead.

- Better treatments -

Several US states and cities have likewise had to roll back their reopening measures. Houston, for example, on Wednesday canceled the Texas Republican Party's upcoming in-person indoors state convention as COVID-19 cases surged in the city.

Having just a handful of cases at the start of February, the US infection rate passed the one million milestone on April 28 and hit two million on June 11, according to an AFP tally of official sources.

All the while, the death toll has been creeping up to its current figure of more than 132,000, almost one-quarter of the global total.

The current US death rate is however substantially lower than it was in late spring.

This is possibly because of a lag between infection and deaths among sick patients, but also because the country's epidemic is affecting younger people, and because better treatments are now available.

Doctors have found that placing patients with breathing troubles on their stomachs eases the burden on their lungs, and are using blood thinners preventatively to stop catastrophic clots from forming as a result of the virus.

They are also using the steroid dexamethasone to stop a supercharged and destructive immune response, and the antiviral remdesivir to help ventilated patients recover faster.

Trump, for his part, has sought to blame China and the World Health Organization for his country's epidemic, and on Tuesday formally began the process of withdrawing from the body. 

His opponent in the November election, former Vice President Joe Biden, has vowed to undo the decision if he wins.  

- 'Extraordinary solidarity' -

The virus continues to take a massive economic toll, sparking an explosion in Canada's federal budget deficit, which hit CAN $343 billion (US $254 billion) for the current fiscal year.

It is equal to 15.9 percent of the Group of Seven nation's gross domestic product (GDP).

The European Union meanwhile is working on a $843 million package to help crisis-hit economies in the bloc.

"We need extraordinary solidarity," said German chancellor Angela Merkel ahead of an upcoming EU summit.

China's new strategy to tame second-wave

A recent coronavirus outbreak in Beijing sowed fears of a second wave of infections in China, but officials appear to have beat back the disease with a new targeted strategy.

Authorities did not repeat the drastic nationwide shutdown seen when the virus first spread from Wuhan earlier this year.

Instead, they sealed off a limited number of residences and focused on mass testing, eventually screening more than half of the capital's 21 million people.

This approach seems to have paid off, with reported cases falling to single digits each day by early July and zero in the past three days.

Here is a look at how China brought the new outbreak under control:

- How did the outbreak begin? -

China went to great lengths to protect its capital at the height of the pandemic, redirecting incoming flights to other cities and requiring visitors to undergo quarantine and virus tests.

But by early June, with just a handful of active cases across the country, Beijing had relaxed many of its restrictions and locals were no longer made to wear masks outdoors.

The emergence of a new patient on June 11 shocked the city.

Most of the 335 subsequent cases were traced to the sprawling Xinfadi wholesale market in southern Beijing, which was swiftly closed.

Thousands of people were placed under quarantine and 11 million people were tested for the virus. 

The city banned outbound travel by residents living in at-risk areas and required others to show negative COVID-19 test results in order to leave.

Authorities are still investigating the cause of the outbreak, but early tests found traces of the virus on a cutting board at Xinfadi used to process imported salmon.

Five million begin lockdown in Australian city

Five million people in Australia's second-biggest city began a new lockdown Thursday, returning to tough restrictions just weeks after they ended as Melbourne grapples with a resurgence of coronavirus cases.

Residents have been told to stay at home for six weeks after other measures to contain a spike in COVID-19 failed to prevent the virus spreading.

The state of Victoria has been effectively sealed off in an effort to preserve the rest of Australia's success in curbing the virus.

However, a rush of travellers across the border into neighbouring New South Wales on Wednesday has raised concerns those efforts could be torpedoed.

"A few cases coming over the border from Victoria (can) tip that magic number into outbreaks that are going to be very hard to control," epidemiologist Mary-Louise McLaws told public broadcaster ABC.

New South Wales Premier Gladys Berejiklian said two cases of COVID-19 had been identified in the border town of Albury and she warned against travel to or from communities on the state frontier.

"We want to make sure that we're flushing out any potential seeding that occurred prior to that spike in cases becoming evident," she told reporters in Sydney.

Queensland state announced Thursday it would turn away all travellers from Victoria -- for the first time removing an option that had allowed them to spend 14 days in quarantine on arrival.

In Melbourne, there are concerns over the economic and mental health impacts of the second lockdown, which officials estimate will cost the economy Aus$6 billion ($4.2 billion).

Restaurants and cafes are limited to serving takeaway food, while gyms, beauty salons and cinemas have been forced to close again.

Residents are restricted to their homes except for work, exercise, medical care or to buy essentials.

Virus overwhelms Venezuelan oil hub

The pain of breathing made butcher Elkin cry. He caught the coronavirus in a street market where he works in Maracaibo, the main city in a once-prosperous oil producing region of Venezuela that has been left destitute by a fuel shortage and frequent blackouts. It's also a virus hotspot.

The outbreak of cases in the western Zulia state that borders Colombia unleashed a "horrible" situation in Maracaibo's Hospital Universitario, a nurse of 15-year experience who asked to be called by her first name, Pilar, told AFP. "We've collapsed," she said.

Several wings of the building have become a "hell" with no air conditioning in an area where temperatures can surpass 40 degrees Celsius (104 degrees Fahrenheit) and which is plagued by blackouts that can last hours, she said.

A lack of water and supplies complete the nightmare scenario for medical professionals, who trudged the hospital corridors drenched in sweat.

"If you don't bring water from your home, you can't wash," Pilar said.

Staff come to work carrying five-litre bottles of water.

The situation is so dire that some 20 patients diagnosed with the novel coronavirus have fled the hospital, she said.

Official figures -- considered improbable by groups such as Human Rights Watch -- show Venezuela's cases jumped from 1,500 on June 1 to 7,000 a month later.

President Nicolas Maduro's government has acknowledged the "worrying" increase.

It took 70 days to reach 1,000 cases from the first one reported, but just four to pass from 6,000 to 7,000.

Zulia, Venezuela's most populous region, accounts for almost a quarter of country's COVID-19 cases.

Venezuela has been battered by seven years of economic recession and soaring inflation. Prices for oil, its main export, remain low, and there is no end in sight to the country's crippling political crisis.