Donald Trump's top expert on coronavirus has warned elderly people with underlying health conditions to restrict their travel and avoid large gatherings.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told NBC's Meet the Press: "If you are an elderly person with an underlying condition, if you get infected, the risk of getting into trouble is considerable. So it's our responsibility to protect the vulnerable.

"When I say protect, I mean right now. Not wait until things get worse. Say no large crowds, no long trips.

"And above all, don't get on a cruise ship."

Dr Fauci said he did not believe the US would have to implement measures as "draconian" as the actions taken in Italy and China to shut down entire towns and cities.

But, he added, "anything is possible".

He told Fox News Sunday: "We have to be realistic. I don't think it would be as draconian as nobody in or nobody out.

"But if we continue to get cases like this, particularly at the community level, there will be what we call 'mitigation', where we have to essentially do social distancing, keep people out of crowded places, take a look at seriousness, do you really need to travel, and I think it's particularly important among the most vulnerable."

He added: "You don't want to alarm people, but given the spread we've seen anything is possible and that's why we've got to be prepared to take whatever action is appropriate to contain and mitigate the outbreak."

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Dr Fauci also rejected claims that the Trump administration had overruled experts on recommending that elderly people should avoid air travel.

More than 400 people across 30 states in the US have been confirmed as having Covid-19, with 19 deaths reported.

On Sunday it was announced that the cruise ship Grand Princess, which has 21 known cases among the more than 3,500 passengers and staff on board, will be allowed to dock in Oakland, California on Monday. Passengers will disembark and be treated or quarantined, while crew will be assessed on board.

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The president said on Friday that he wanted passengers and employees to remain on board so that the number of cases in the US did not go up "because of one ship that wasn't our fault".