WASHINGTON (REUTERS) - Signs that coronavirus is spreading through US communities were "not encouraging" and a top health official warned on Sunday (March 8) that Americans, especially those who are vulnerable, may need to stop attending large gatherings.

In the United States, 19 people have died and more than half of all states have reported cases of the coronavirus, which originated in China last year and causes the sometimes deadly respiratory illness Covid-19.

As the outbreak takes root, daily life has become increasingly disrupted, with concerts and conferences cancelled and universities telling students to stay home and take classes online.

"I think we're getting a better sense (of the scope of the outbreak) as the days go by," Dr Anthony Fauci, the head of the infectious diseases unit at the National Institutes of Health, said on NBC's Meet the Press.

"Unfortunately, that better sense is not encouraging because we're seeing community spread," he said.

He urged those most at risk from coronavirus to limit travel.

"If you're a person with an underlying condition and you are particularly an elderly person with an underlying condition you need to think twice about getting on a plane, on a long trip, and not only think twice, just don't get on a cruise ship," Dr Fauci said on Meet the Press.

Dr Fauci said that in addition to efforts to try to contain the spread of the virus, it was important to start thinking about how to mitigate the impact as more and more Americans fall ill.

"They call it 'social distancing', but it is common sense stuff," he said. "You don't want to go to a massive gathering, particularly if you are a vulnerable individual."

The hardest hit area has been a nursing home in a suburb of Seattle.

The United States is also preparing to take some passengers off a cruise ship that was barred from docking in San Francisco after several people aboard tested positive for the virus.