The World Health Organization has urged countries grappling with coronavirus to step up control measures, saying it is still possible to rein it in, as some nations clamp fresh restrictions on citizens.

With case numbers worldwide more than doubling in the past six weeks, Uzbekistan on Friday returned to lockdown and Hong Kong said schools would close from Monday after the city recorded "exponential growth" in locally transmitted infections.

WHO chief Tedros Adhanom Ghebreyesus called on countries to adopt an aggressive approach, highlighting Italy, Spain, South Korea and India's biggest slum to show it was possible to stop the spread, no matter how bad the outbreak.

The health agency's comments came as US President Donald Trump was forced to cancel an election rally in New Hampshire, citing an approaching storm.

Trump has pushed to hold large gatherings against health advice as epidemiologists warn of the dangers posed by the virus moving through the air in crowded and confined spaces.

- Lashing out at China -

On a visit to Florida on Friday, Trump hit out at Beijing over the pandemic.

"(The) relationship with China has been severely damaged. They could have stopped the plague.... They didn't stop it," he told reporters.

The virus has killed at least 556,140 people worldwide since it emerged in China last December.

More than 12.3 million cases have been registered in 196 countries and territories, triggering massive economic damage.

The United States, the country worst hit by the illness, reported almost 64,000 new cases Friday and the death toll now stands at just under 134,000, according to Johns Hopkins University.

Brazil, the second-hardest hit, surpassed 70,000 deaths and reported 45,000 new infections, the health ministry said.

In Uzbekistan, citizens were from Friday facing lockdown restrictions again that were originally imposed in March but lifted gradually over the past two months.

The Central Asian country's return to confinement followed a decision by Australia to lock down its second-biggest city Melbourne from Thursday.

A police officer manning a checkpoint on the outskirts of the former Soviet republic's capital said only drivers with "a good reason" to enter Tashkent -- such as delivering food or other vital supplies -- could pass.

Restaurants, gyms, swimming pools and non-food markets have all shut their doors until at least August 1.

Private transport within cities will be limited to morning and early evening journeys and essential purposes such as travelling to work and purchasing food or medicine.

In Hong Kong, the spike marks a setback for the city after daily life had largely returned to normal with restaurants and bars resuming regular business and cultural attractions reopening.

Despite being right next to mainland China where the virus first emerged, the city had managed to quash local transmission in recent months.

But new clusters have started to emerge since Tuesday, including at an elderly care home that reported at least 32 cases and a housing estate with 11.

- 'Turn this pandemic around' -

"Across all walks of life, we are all being tested to the limit," the WHO's Tedros told a virtual news conference in Geneva.

"From countries where there is exponential growth, to places that are loosening restrictions and now starting to see cases rise.

"Only aggressive action combined with national unity and global solidarity can turn this pandemic around," he said.

Elsewhere, French officials warned of rising cases in metropolitan France as the death toll topped 30,000.

In Israel, Prime Minister Benjamin Netanyahu admitted a decision to allow businesses, including bars and event spaces, to reopen may have been made "too soon".

The Middle Eastern country recorded its highest number of infections over a 24-hour period, at nearly 1,500.

In Australia, meanwhile, authorities said they would slash by half the number of people allowed to return from overseas.

From Monday, only 4,000 Australian citizens or permanent residents will be permitted to enter each day.

US records 63,643 new cases

The United States recorded 63,643 new coronavirus cases on Friday, according to a tracker maintained by Johns Hopkins University.

As of 8:30 pm (0030 GMT Saturday), 774 people died of COVID-19 in the country in the past 24 hours, the Baltimore-based university said. 

The worst-hit country in the world by the pandemic, the US has recorded a total of 133,969 deaths out of 3.18 million cases.

Thursday saw a record surge in cases, with 65,551 new infections. Experts fear there will soon be a spike in deaths.

In recent days, Texas and Florida reported record numbers of virus deaths.

"As a country, when you compare us to other countries, I don't think you can say we're doing great," top infectious disease official Anthony Fauci told political analysis website FiveThirtyEight on Thursday.

President Donald Trump, for his part, hit out at the respected scientist, telling Fox News: "Dr Fauci is a nice man, but he's made a lot of mistakes."

The US leader, who continues to downplay the spike in coronavirus cases, traveled to outbreak hotspot Miami on Friday for a high-dollar campaign fundraiser and other events.

Brazil surpasses 70,000 deaths

Brazil surpassed 70,000 coronavirus deaths on Friday, the health ministry said, though the number of daily fatalities appears to be stabilizing.

The ministry said there had been 45,000 new infections and 1,200 deaths over the last 24 hours, taking the totals to 1.8 million cases and 70,400 deaths.

Brazil, a country of 212 million, is the second worst-affected country in the world after the United States.

The number of deaths has doubled over the last 35 days with Sao Paulo and Rio de Janeiro states the worst hit, respectively reporting 17,400 and 11,200 deaths.

In relative terms, though, Brazil has registered 335 deaths per million inhabitants, which is less than the US with 403 or Spain's 607.

However, in some states, such as Rio de Janeiro (653), Ceara (742) and Amazonas (726), the figures are way over the national average.

In four of the last five weeks, Brazil averaged more than 1,000 deaths a day.

Despite the outbreak showing no sign of slowing down, several states, including Rio and Sao Paulo, have started relaxing containment measures.

In Rio, bars overflowing with people and crowds crammed onto beaches have caused much concern.

"Our projections show that in this scenario, the number of cases will keep rising until October-November, with fluctuations," Domingos Alves, Health Intelligence Laboratory coordinator at the Riberao Preto faculty of medicine in Sao Paulo, told AFP.

"It will be an effect of relaxing (confinement measures), contrary to the evidence collected by all the countries following World Health Organization recommendations.

"It won't be about a second wave but rather an extension of the first one."
Panama hospitals on verge of collapse

Hospitals in Panama are on the brink of collapse as coronavirus cases spike in the Central American country worst hit by the pandemic, where doctors are already exhausted.

With a population of four million, Panama has gone from 200 cases a day to 1,100 over the last few weeks.

"Our daily number of infected patients has been increasing in a sustained way to the point of passing 1,000 cases," David Villalobos, head of the intensive care unit at the Arnulfo Arias Madrid Hospital in Panama City, told AFP.

"There are no hospitals that could sustain such a number," he said.

The sharp increase has forced authorities to adapt existing hospitals and look for new spaces, like convention centers, to boost a health system with a range of problems including long waiting lists.

"The fear of the collapse of the public system in our country is evident if the number of cases remains the same," Domingo Moreno, coordinator of a coalition of healthcare workers' unions, told AFP.

"In the next two weeks we probably won't have anywhere to put beds."

With 42,000 cases and 839 deaths, Panama has the worst official tally of coronavirus infections in the region.