Employees of Russia’s Emergency services disinfect a platform of Leningradsky railway station in Moscow on Tuesday. AP

President Donald Trump has threatened to pull the US out of the World Health Organisation (WHO), accusing it of botching the global coronavirus response and of being a "puppet of China" − prompting rebuke from Beijing which said on Tuesday Washington was "shirking responsibility."

Trump has been locked in a bitter spat with Beijing, alleging it covered up the initial outbreak in central China late last year before the disease unleashed death and economic devastation across the planet.

Some 317,000 people have died of COVID-19 out of nearly 4.8 million infections worldwide, and governments are scrambling to contain the virus while seeking ways to resuscitate their hammered economies.

With more fatalities and cases in the United States than any other country by far, the under-pressure US president has blamed the WHO for not doing enough to combat its initial spread.

"They're a puppet of China, they're China-centric to put it nicer," he said on Monday at the White House.

"They gave us a lot of bad advice."

Trump had already suspended US funding to the UN body, and after his White House comments, he tweeted a letter he had sent to WHO chief Tedros Adhanom Ghebreyesus threatening to make that freeze permanent.

Donald Trump speaks during a meeting in the State Dining Room of the White House on Monday. AP

"It is clear the repeated missteps by you and your organisation in responding to the pandemic have been extremely costly for the world," the letter said.

"The only way forward for the World Health Organisation is if it can actually demonstrate independence from China," it added, giving the body 30 days to show "substantive improvements."

Beijing has furiously denied the US allegations that it played down the threat, and Chinese President Xi Jinping reiterated at the World Health Assembly that his nation had been "transparent" throughout the crisis.

Beijing said on Tuesday Trump was trying to "smear China" over its international obligations to the WHO.

"The US tries to use China as an issue to shirk responsibility and bargain over its international obligations to the WHO. This is a miscalculation and the US has picked the wrong target," foreign ministry spokesman Zhao Lijian said.

The WHO's main annual assembly was due Tuesday to discuss a resolution tabled by the European Union calling for an "impartial, independent and comprehensive evaluation" of the international response to the COVID-19 pandemic and the measures taken by the UN agency.

Countries reached an agreement in principle last week to accept the text unanimously, but amid rising political tensions some observers expressed fears that full consensus might not be obtained.

As he launched his latest attack on China, Trump also dropped a bombshell saying he was taking hydroxychloroquine, an anti-malaria drug that his own government's experts have said is not suitable for fighting the coronavirus.

"I take a pill every day," said the president, adding that he is using it because he has "heard a lot of good stories."

Experts have warned that the social distancing measures that have impacted more than half of humanity will remain necessary to stop the virus until a vaccine or viable medical treatment is available.

Development work on a prophylactic is under way at breakneck speed around the world, and results from a trial in the United States sparked optimism on Monday.

Early − and small − clinical trials of a vaccine by US firm Moderna showed encouraging results, with recipients showing an immune response similar to people recovering from COVID-19. It will begin a larger second-phase trial soon.

In China, meanwhile, scientists at Peking University have said they are developing a drug that can help stop the pandemic without a vaccine by using antibodies that can neutralise the virus.

They are planning clinical trials for the treatment, and are hoping to have the drug available later this year and in time for any potential winter outbreak.

Authorities around the world are keeping an eye on such breakthroughs as the virus continues on its destructive path, with many poorer nations now seeing a dramatic rise in infections even as the caseload eases in more developed parts of the world like Europe.

In Russia, the number of coronavirus cases hit nearly 300,000 on Tuesday after Moscow said the virus situation had stabilised.

The Kremlin also said Prime Minister Mikhail Mishustin is returning to his duties after fighting off the coronavirus.

Agence France-Presse