Australia's worst-hit state of Victoria reported 15 coronavirus deaths on Wednesday, including a man in his 30s, making it the country's deadliest day of the pandemic to date.

An outbreak in Melbourne, Australia's second-biggest city and the capital of Victoria, has seen hundreds of new cases recorded daily in recent weeks, including 725 on Wednesday.

The epidemic surge continued even though Melbourne has been under a stay-at-home lockdown for nearly a month.

Victoria Premier Daniel Andrews told a press conference that the latest fatalities included one man in his 30s and 12 other deaths linked to care homes for the elderly.

The virus has spread rapidly through nursing homes in the city, with almost 1,500 active infections now linked to the facilities.

Authorities imposed an overnight curfew in Melbourne from Monday, have closed non-essential businesses and ordered mandatory mask-wearing as authorities try to bring the outbreak under control.

Andrews said all but the most urgent elective surgeries would now be postponed "until further notice" to ease the strain on hospitals.

"The sickest patients must get treated quickest," he said.

"This is a regrettable decision but it is very important one in order to preserve sufficient capacity in our entire health system."

Australia has now recorded more than 19,000 cases of coronavirus and 247 deaths from the virus.

Victoria has been effectively sealed off from the rest of the country, with residents banned from visiting leaving except in limited circumstances.

Other states and territories are continuing to detect few or no new daily cases.

US adds 1,300 virus deaths

The US on Tuesday added 1,302 deaths from COVID-19 in the past 24 hours, according to a tally by Johns Hopkins University.

The world's largest economy also added 53,847 new cases of the virus, the Baltimore-based institution's tracker showed at 8:30 pm (0030 GMT Wednesday).

The US has now recorded 4,765,170 total cases with 156,668 deaths, making it by far the worst-hit country in the world.

But President Donald Trump adopted a resolutely optimistic tone.

"We're seeing indications that our strong mitigation efforts are working very well, actually, especially to protect those who are most at risk," he said during a White House press conference addressing the pandemic.

Trump resumed his almost daily coronavirus briefings after case levels began to spike in parts of the southern and western United States at the end of June.

The billionaire Republican has attributed the rise in reported case numbers to an increase in testing, insisting that "the United States is testing more people in a single week than, in many cases, large segments or large well-known countries all put together."