Indonesia was expected to pass the 50,000 mark for confirmed infections on Thursday. In Melbourne, health workers planned to go door-to-door to test more than 100,000 residents in a coronavirus hotspot that threatens to undo the nation's success in battling the virus.

In the Indian capital of New Delhi, which has reported more than 70,000 cases, authorities said they would conduct house-to-house screening. India reported a record high 16,922 cases on Thursday, taking the national total to 473,105, with nearly 15,000 deaths.

World financial markets were rattled by the setbacks in fighting the pandemic, which cloud prospects for recoveries of economies mired in their worst downturn since the Great Depression of the 1930s.

Asian shares fell Thursday after the Dow Jones Industrial Average lost over 700 points overnight for a drop of 2.7 per cent and the broader S&P 500 fell 2.6 per cent.

In China, where the virus first appeared late last year, an outbreak in Beijing appeared to have been brought under control. China reporting 19 newly confirmed cases nationwide amid mass testing in the capital. Case numbers both nationally and in Beijing were up by only single digits from Wednesday.

South Korea was still struggling to quell an outbreak, reporting 28 new cases on Thursday, mostly associated with nightlife, churches, a huge e-commerce warehouse and door-to-door sales. But the numbers have not reached the hundreds of new cases every day in late February and early March.

While some governments are considering more aggressive action to stem fresh outbreaks, in other places such precautions are being unwound.

Dubai, in the United Arab Emirates, ended a months-long nightly curfew, with the city-state's media office tweeting there would be "free move all day & night" as long as people wore masks and maintained social distancing.

European nations appeared on track to reopen their shared borders by July 1 and their EU representatives debated criteria for lifting restrictions on visitors from outside Europe.

Americans are unlikely to be allowed in, given how the pandemic is flaring in the US and President Donald Trump's ban on Europeans entering the United States.

American hospital administrators and health experts warned Wednesday that politicians and a public tired of being cooped up are letting a disaster unfold. The 34,700 COVID-19 cases reported Tuesday returned the US to near its late April peak of 36,400 new cases in one day, according to a Johns Hopkins University count.

New York state, New Jersey and Connecticut, which were devastated by early outbreaks that appear to be under control, have announced they will require travellers from certain states to quarantine for 24 days upon arrival.

Several states have set single-day case records this week, including Arizona, California, Mississippi, Nevada, Texas and Oklahoma. Some also broke hospitalisation records, as did North Carolina and South Carolina.

The virus has been blamed for more than 120,000 US deaths - the highest toll in the world - and more than 2.3 million confirmed infections. The widely cited University of Washington computer model of the outbreak projects nearly 180,000 deaths by October 1.

Alarmed, some states are moving to ensure more consistent use of face masks and other anti-virus measures.

North Carolina has ordered people to wear masks in public as the daily count of hospitalisations and new cases hovers near records. In Florida, several counties and cities recently enacted mask requirements.

Nevada will require use of face-coverings in public places to stem rising infections after casinos, restaurants and other businesses started reopening.

Worldwide, more than 9.4 million people have been confirmed infected and nearly 500,000 have died, by Johns Hopkins' count.

Dr Michael Ryan, the WHO's emergencies chief, said when countries would hit their peak numbers of infections hinges entirely on what people did: "There are no magic answers ... You can't divine this away. We have to act at every level."

Australian Associated Press