The United States reached 400,000 confirmed coronavirus cases on Wednesday according to the Johns Hopkins University tally, a grim milestone that comes as the death tolls continue to rise in hot spots in what experts expect to be the country's deadliest week so far.

The US set another record with 1,850 deaths in a single day on Tuesday, the highest single-day total of any country. By Wednesday, more than 14,500 deaths had been reported nationwide.

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Italy and Spain both still outpace the US in total deaths, with roughly 17,000 and 12,000 respectively.

US health officials have warned that between 100,000 and 200,000 people in the country are likely to die from COVID-19, the disease the virus causes. But officials said this week that despite the grim totals, there are signs that the death toll may not be as high as expected if mitigation efforts continue.

The World Health Organization (WHO) declared the virus a global health emergency on January 30 and a pandemic on March 11.

The US had its first known case of the novel coronavirus in January. By March, US health officials warned of a serious threat to the public.

States began issuing shelter-in-place orders and cancelling classes in an effort to "flatten the curve", or limit the spread of the virus to give hospitals a chance to treat those infected.

The US Congress passed on March 27 a significant $2.2 trillion rescue bill, called the CARES Act to aid prevention efforts and offer a lifeline to struggling businesses and individuals.

The administration of President Donald Trump has at times been lauded and scorned for its handling of the pandemic.

At first, Trump said warm weather in April could make the virus disappear, remarks that were widely criticised.

After the passage of the CARES Act and daily news conferences with top health officials, such as Dr Anthony Fauci, the public began to trust the president with his approval ratings reaching new heights.

However, states have aired grievances with the federal government, saying Washington is not offering needed medical supplies.

New York Governor Andrew Cuomo has repeatedly stated that states are bidding for ventilators on an open market akin to online auction site eBay.

Trump dismissed the claims, saying the US and his administration are handling the outbreak better than anyone else.

Cuomo said on Wednesday that despite high death toll, "there is no doubt" the state is bending the curve.

New York recorded its highest daily death toll - 779 - on Tuesday. The state's death toll increased by 731 the day before.

"Don't start doing a retrospective like it's over," Cuomo told a daily briefing on the states' coronavirus response, urging residents to stay at home as much as possible. "We are not through it. It's not over."

Return to normalcy?

Fauci, the top US infectious diseases expert, told Fox News on Wednesday that health officials are planning ways for the country to return to normal activities if distancing and other steps to mitigate COVID-19 this month prove successful in curbing the outbreak.

The Trump administration has called for 30 days of measures, including staying at least 1.8 metres (six feet) away from other people, that have upended American life.

Fauci, director of the National Institute of Allergy and Infectious Diseases, said such steps must continue but that there are hopeful signs they are working.

"If in fact we are successful, it makes sense to at least plan what a re-entry into normality would look like. That doesn't mean we're going to do it right now, but it means we need to be prepared to ease into that," Fauci said.