New York's Governor Andrew Cuomo says the rate of new hospitalisations has fallen over the past two days.

The rate of hospitalisations in New York state, the epicentre of the US outbreak, has slowed in recent days, said Governor Andrew Cuomo, with numbers that he called "almost too good to be true."

But New Orleans, where large crowds last month celebrated Mardi Gras, was on track to become the next US epicentre, with the world's highest growth rate in coronavirus cases.

Despite the encouraging news, Governor Cuomo said New York City, home to more than 8 million people, would close some public streets to vehicles, opening them up to pedestrian traffic to facilitate "social distancing" to avoid infections.

He told a news conference the city would ban basketball and other contact sports in parks, first on a voluntary basis as long as people comply.

"Our closeness makes us vulnerable," said Governor Cuomo, who has emerged as a leading national voice on the coronavirus.

Governor Cuomo said more than 30,800 people had tested positive for the virus in his state and more than 17,800 in New York City alone.

The state has reported 285 deaths and roughly half the country's reported infections. The state was among the earliest to close non-essential businesses and take other measures to keep people apart to prevent infections.

Hospitalisations were doubling every two days as of Sunday, but by Monday the trend showed hospitalisations were doubling every 3.4 days, and by Tuesday the rate was 4.7 days, Governor Cuomo said.

"This is a very good sign and a positive sign, again not 100 per cent sure it holds, or it's accurate but the arrows are headed in the right direction," he said.

Twitter; Andrew Cuomo

@NYGovCuomo

Evidence suggests density control plan may be working:

On Sun, hospitalizations doubling every 2 days

On Mon, hospitalizations doubling ever 3.4 days

On Tues, hospitalizations doubling every 4.7 days

But the virus is STILL spreading quickly. #StayAtHome

Testing for the virus remained a challenge in New York and around the United States.

At Elmhurst Hospital Centre, which serves about 1 million people in New York's Queens borough, scores of people, most wearing surgical masks, queued up on Wednesday to be tested at a special tent set up outside.

The White House on Tuesday advised people who had visited or left New York to isolate themselves for 14 days, but Governor Cuomo and his medical adviser played down that White House advice.

Nationwide, about 60,000 people have been diagnosed with COVID-19, the disease caused by the virus that is particularly perilous to the elderly and people with pre-existing medical conditions, with at least 812 U.S. deaths.

The impact was increasingly being felt beyond the hot spots of New York, California and Washington state as Louisiana and others faced a severe crush on their healthcare systems.

Five states have received major disaster declarations from the Republican president. New York, the state with by far the most infections and deaths, was given such status last weekend as well as California and Washington state.

President Donald Trump on Tuesday said he wanted to reopen the country by Easter Sunday, far sooner than public health officials have said is warranted, but later told reporters he would listen to recommendations from the nation's top health officials.