The US State Department has warned citizens not to take a cruise, particularly the elderly with existing medical conditions.
The stark warning comes as 21 crew and passengers were diagnosed with the virus aboard the Grand Princess ship which remains moored off the west coast.
The ship will dock in a non-commercial port in Oakland.
Authorities said it could take two days to fully disembark all passengers.
"If you’re a senior citizen with a serious underlying health condition, this would be a good time to practice common sense and to avoid activities including traveling on a cruise line," vice president Mike Pence said.
The State Department advisory said: "This is a fluid situation. CDC notes that older adults and travelers with underlying health issues should avoid situations that put them at increased risk for more severe disease. This entails avoiding crowded places, long plane trips, and especially avoiding embarking on cruise ships."
It is likely to severely damage the cruise industry short term, as seniors make up a sizable proportion of cruise traffic.
The three big cruise companies saw shares tumble again.
It will also have major impact across the Caribbean where many nations are heavily reliant on the US cruise market.
The warning was echoed by several senior health officials and lawmakers including California Governor Gavin Newsom.
"If you are elderly, if you have a pre-existing condition… I would highly recommend, almost demand that you not go on a cruise," Newsom said.
