Health officials say 21 people on a cruise ship barred from docking in San Francisco have tested positive for coronavirus, as half a dozen US states reported their first cases of the fast-spreading respiratory disease.
Four Australians are among those on board.
Vice President Mike Pence, who is running the White House's response to the outbreak, said 19 crew members and two passengers had the virus out of 46 people tested so far had the virus.
He said the vessel, called the the Grand Princess, which has around 3,400 passengers and crew, would be taken to a non-commercial port where everyone on board would be tested.
US President Donald Trump said he would rather have passengers remain on board the vessel, but that he would let others make the decision whether to let the passengers disembark.
"I'd rather have them stay on, personally, but I fully understand if they want to take them off," Mr Trump told reporters after touring the Centres for Disease Control and Prevention (CDC) in Atlanta.
Keeping passengers quarantined aboard a coronavirus-hit ship proved to be a disastrous strategy in Japan, leading to one of the world's biggest outbreaks.
Mr Trump earlier signed a bill that will provide $8.3 billion to bolster the country's capacity to test for coronavirus and fund other measures to stem an outbreak that has now killed 15 Americans.
On Friday, six states - Pennsylvania, Indiana, Minnesota, Kentucky, Oklahoma and Nebraska - reported their first cases, bringing the total to 25 states that now have the virus.
In Seattle, the epicentre of the nation's outbreak, there were school closures and orders to work from home. In Miami and Baltimore, areas less affected by the outbreak, music festivals and sporting events were cancelled or curtailed as a precaution.
As stocks plunge and US companies grapple with the economic fallout, the Trump administration is said to be weighing tax relief for the deeply affected cruise, travel and airline industries.
Americans are sharply divided over the dangers of the new coronavirus, according to a Reuters/Ipsos poll.
Critics of Mr Trump have accused the president of downplaying the significance of the outbreak for political reasons. He has said the risk to Americans is low.
Source: 9News https://www.9news.com.au/world/coronavirus-grand-princess-cruise-passengers-test-positive-california-usa-news/4dc48521-11cc-44c4-8179-b1643def9186