"I am asking healthcare professionals across the country, if you don't have a healthcare crisis in your community, please come help us in New York now," Andrew Cuomo told a news briefing in a makeshift hospital in Manhattan on Monday.

Cuomo said the state's doctors and nurses needed relief and vowed to "return the favour" when there is "an intense issue somewhere else in the nation".

"What is happening to New York is not an anomaly," he warned, as hotspots also emerged in Louisiana, California and Illinois.

"The numbers are already staggering ... We've lost over 1,000 New Yorkers."

But in a hopeful note, he said that while the number of hospitalisations continues to rise, the rate at which it is growing is tapering off, doubling every six days compared with every two or three days before.

The governor also hit back at US President Donald Trump's suggestion that New York hospitals were squandering protective gear, saying the state is creating a stockpile of supplies to prepare for the "apex" of the outbreak.

Cuomo said he was not going to "rise to the bait of a political challenge".

Later on Monday, Trump announced that more than a million people were tested for the novel coronavirus in the US.

"Today we reached a historic milestone in our war against the coronavirus," Trump said at a news briefing at the White House. "Over one million Americans have been tested - more than any other country by far."

Health Secretary Alex Azar said nearly 100,000 tests were being carried out per day.

The Trump administration has come under fire for its slow rollout of tests and state governors continue to complain about a lack of testing capacity.

Trump also suggested so many US companies were now producing ventilators that the country would soon "outpace what we need" and send supplies to hard-hit European countries, including Italy, Spain and France.

Meanwhile, John Bel Edwards, the governor of Louisiana, where the death toll jumped about 20 per cent overnight to reach 185 on Monday, said ventilators remain the states "most pressing need" and every state needed more testing capacity.

Earlier on Monday, a 1000-bed hospital ship docked in Manhattan to help relieve the New York City's overwhelmed hospitals by treating patients who do not have the virus.

"This is like adding another hospital here in New York City," Mayor Bill de Blasio said. "The nation has heard our pleas for help."

But he acknowledged the city needs to triple its hospital bed capacity by May.

Pictures also showed a small field hospital being erected in tents in the city's famous Central Park.

So far there have been more than 2900 deaths and some 160,000 confirmed cases in the US, according to Johns Hopkins University data.

Australian Associated Press