At least 21 people have now died in the United States from the coronavirus as it spread to 30 states with hundreds of confirmed cases nationwide.

Oregon was the latest to declare a state of emergency on Sunday, and 60 million people in California and New York states faced crisis measures.

Two more deaths were reported in Washington state - both linked to a virus-hit care home near Seattle - bringing the nationwide toll to at least 21.

Americans, especially those who are vulnerable, may need to stop attending large gatherings as the coronavirus spreads through US communities, a top health official said on Sunday.

Anthony Fauci, head of the infectious diseases unit at the National Institutes of Health, said on NBC's Meet the Press that after initial missteps distributing tests, there should be 400,000 more tests available by Monday and four million by the end of the week.

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About 500 US cases have been reported of coronavirus, which originated in China last year and causes the sometimes deadly respiratory illness COVID-19. The outbreak has killed more than 3,700 globally.

More than half of the 50 US states have reported cases, including the first ones in Virginia and Connecticut on Sunday.

Fauci downplayed the likelihood of the type of large-scale quarantines put in place in China and Italy, while saying nothing could be ruled out.

"I don't imagine that the degree of the draconian nature of what the Chinese did would ever be either feasible, applicable, doable or whatever you want to call it in the United States," he said in an interview on CBS' 60 Minutes.

"But the idea of social distancing, I mean, obviously, that's something that will be seriously considered," he said, urging those most at risk to limit travel.

US Surgeon General Jerome Adams said cases would rise, adding the average age of death for people with the virus was 80, and the average age of those needing medical attention was 60.

"Unfortunately, you are going to see more deaths, but that doesn't mean that we should panic," he said.

Testing positive

New York Governor Andrew Cuomo said the number of cases in New York state is now 105 and he expects that to rise as testing expands.

District of Columbia Mayor Muriel Bowser said on Saturday that a man in his 50s tested positive for coronavirus in Washington, DC. Another person - also in his 50s and living in Nigeria - who travelled through the city, has also tested positive in Maryland, Bowser said.

Jennifer Smith, who leads Washington's public health laboratory, said officials had the capability to test about 50 patients per day. The district has also ordered more than 42,000 masks to be delivered to the district's fire and emergency medical workers, officials said.

Virginia recorded its first case on Saturday when a US Marine stationed at Fort Belvoir was found to have the virus.

To contain the epidemic, concerts, festivals and other public events have been cancelled across the US.

Grand Princess to dock

Meanwhile, the Grand Princess, a coronavirus-stricken US cruise ship, has been given permission to dock in Oakland, California, the tour operator said in a statement on Saturday.

"Grand Princess will proceed to the Port of Oakland on Sunday to begin disembarking guests who require acute medical treatment and hospitalisation," the Princess Cruises tour company said.

The vessel, which has been stranded off the California coast for four days, recorded 21 cases on board, including 19 crew and two American passengers.

The cruise ship, barred from returning to San Francisco last week because of a coronavirus outbreak on board, will send its 2,400 passengers to at least four quarantine centres. The crew of 1,100 will be quarantined and treated on board the ship.

The hardest hit place in the United States has been a nursing home in a suburb of Seattle and Washington state is considering mandatory measures such as banning large gatherings but not necessarily imposing massive quarantines, the governor said.

Oregon state announced seven new cases on Sunday and the governor announced a state of emergency.

Trump 'not concerned'

President Donald Trump defended the "perfectly coordinated" US response to the coronavirus epidemic Sunday amid heavy criticism over health cuts and strategic blunders that have failed to stem its rapid spread.

Trump, who has been accused of peddling misinformation on the outbreak, blamed the media in a tweet for trying to make his government "look bad" as criticism mounted with nearly 500 cases recorded.

But Larry Hogan, the Republican governor of Maryland, criticized Trump, telling NBC the president "hasn't communicated the way I would, and the way I might like him to."

New York Governor Andrew Cuomo said federal health authorities had been "caught flat-footed" and had "handcuffed" the ability of individual states to respond.

"Their messages are all over the place, frankly," he told Fox News.