WASHINGTON (AFP) - America's top infectious diseases official has raised concerns over the safety of Covid-19 vaccines being developed by China and Russia as the world scrambles for answers to a pandemic the WHO warned will be felt for decades.

Six months after the World Health Organisation declared a global emergency, the novel coronavirus has killed at least 679,000 people and infected at least 17.9 million, according to an AFP tally.

As countries across Western Europe announced new lockdowns and reported historic economic slumps, the UN health body said the pandemic was a "once-in-a-century" crisis and its fallout would be felt for decades.

Several Chinese companies are at the forefront of the race to develop an immunity to the disease and Russia has set a target date of September to roll out its own vaccine.

But US infectious disease expert Anthony Fauci said it was unlikely his country would use any vaccine developed in either country, where regulatory systems are far more opaque than they are in the West.

"I do hope that the Chinese and the Russians are actually testing the vaccine before they are administering the vaccine to anyone," he told a US Congressional hearing on Friday.

"Claims of having a vaccine ready to distribute before you do testing, I think, is problematic, at best."

Last month, Chinese media announced a coronavirus vaccine developed by CanSino Biologics was being used to immunise the Chinese military - making it the first approved for people, albeit in a limited population.

Many scientists however raised ethical concerns because the vaccine has not yet begun its final stages of testing.

As part of its own "Operation Warp Speed," the US government will pay pharma giants Sanofi and GSK up to $2.1 billion (S$2.8 billion) for the development of a Covid-19 vaccine, the companies said.

In east Asia, territories which saw success in tackling the early wave of the coronavirus are now confronting worrying new spikes.

Japan's Okinawa declared a state of emergency Saturday after a record jump in cases on the island - many linked to US military forces stationed there - while Hong Kong opened a new makeshift hospital to house Covid-19 patients.

The finance hub had been a poster child for tackling the coronavirus, with local transmissions all but ended by early summer.

But since July daily cases have risen to record highs, partly brought in by the tens of thousands of people who were exempted from a mandatory quarantine imposed on most arrivals.

'SPUTNIK MOMENT'?

Two other Chinese companies Sinovac and Sinopharm, have launched final phase three trials in Brazil and the United Arab Emirates, respectively.

China, where the virus originated, has largely brought its outbreak under control and has therefore had to turn to other countries to test its vaccines.

The trials in Brazil and the UAE will be watched particularly closely, given China's history of vaccine and other health scandals.

In 2018, more than 200,000 children were administered a defective vaccine for diphtheria, tetanus and whooping cough (DPT) that caused paralysis in a few cases.

Russia, which was once a global vaccine leader during Soviet times, aims to bring two to market by September and October, respectively.

The first is being developed by the Moscow-based Gamaleya institute and the defense ministry, and the second by the Vektor state laboratory near the Siberian city of Novosibirsk.

Russia has released no scientific data proving the vaccines' safety or efficacy.

Nevertheless, Kirill Dmitriev, the head of Russia's sovereign wealth fund which is financing the Gamaleya trials, told CNN: "It's a Sputnik moment."

Sputnik was the world's first satellite launched by Russia in 1957.

Three Western coronavirus vaccines are in final phase three trials.

One is produced by US biotech firm Moderna and the National Institutes for Health; one by the University of Oxford and Britain's AstraZeneca; and the last by Germany's BioNTech with US pharmaceutical Pfizer.

China and Russia both stand accused of attempting to steal Western coronavirus research - charges they deny.