US President Trump tweeted on Saturday night (US time) that he has asked the Centres for Disease Control and Prevention to issue a "strong Travel Advisory" but that a quarantine on the New York region "will not be necessary."

Earlier in the day Trump had said that he might order a quarantine for the area, a possibility that New York Governor Andrew Cuomo (D) called "preposterous".

The decision was made at the recommendation of the White House coronavirus task force and in consultation with the governors of New York, New Jersey and Connecticut, Trump said.

He said the travel advisory would be administered by governors "in consultation with the federal government." Full details will be released by the CDC later on Saturday, he added.

New York has become the epicentre of the coronavirus pandemic in the United States, with New York reporting more than 50,000 confirmed coronavirus cases and more than 700 deaths Saturday. New York City alone has seen 200-plus deaths in the last 24 hours, according to local officials.

But Cuomo had questioned the legality of the strict new measure Trump floated to contain the outbreak in the region.

"This would be a declaration of war on states, a federal declaration of war, and it wouldn't just be New York, New Jersey, Connecticut," Cuomo said earlier Saturday. "Next week it would be Louisiana with New Orleans, and the week after that it would be Detroit and Michigan, and it would run across the nation."

Meanwhile, confirmed US coronavirus-related deaths doubled in two days, hitting 2,000 on Saturday evening, based on reporting from state health departments. Also, the United States has gone over 20,000 officially announced new cases in one day for the first time.

It took about a month from the first confirmed death for the United States to record 1,000, but the toll has risen rapidly, and officials say the worst is yet to come. The earliest death was announced in Washington state on February 29.

For the first time, more than 20,000 new infections were announced in a day, pushing the nation's total past 120,000.

• Covid19.govt.nz: The Government's official Covid-19 advisory website

The sharp rise in confirmed cases and fatalities comes as the pandemic's epicentre has shifted to the United States and as health professionals and officials countrywide sound alarms that hospitals are not prepared for an influx of coronavirus patients.

Globally, confirmed cases now exceed 650,000, according to a Johns Hopkins University tracker.