Coronavirus testing kits are being airlifted to a cruise ship quarantined in waters off San Francisco with 140 Britons on board.
US officials ordered that the Grand Princess be held off the California coast after a passenger on an earlier trip died and at least one other was infected with Covid-19.
A Coast Guard helicopter was due to deliver test kits to the ship on Thursday once it reached waters off San Francisco, with test results expected on Friday.
The ship has a capacity of 3,650 passengers and crew but Princess Cruises said fewer than 100 had been identified for testing.
The cruise line said that no cases of the virus had been confirmed among those still on the ship but that some passengers had experienced flu-like symptoms.
Passenger Sharon Lane, from the UK, told CNN she was worried about the elderly guests on board who may be more vulnerable to coronavirus.
“People are starting to get worried, and especially on this cruise,” she said. “On this cruise, it's mainly really elderly people.”
A fellow passenger from Granbury in Texas, told Radio 4’s Today programme that she hadn’t seen anyone who looked visibly ill.
She said: “I don’t see anybody walking around that appears sick. There may be some, if they are they must be in the medical area. Nobody is walking around sneezing and coughing
“People are I’m sure a little bit anxious but nobody has gone screaming mad yet.”
The Grand Princess was on a 15-day trip that was cut short after news broke that a man who had been on a previous trip died after contracting the illness.
In a statement Princess Cruises said: “Public health officials have advised that no guests will be permitted to disembark until all (test) results have been received.
“While there are no confirmed cases of COVID-19 currently on board, the CDC has identified groups of guests and crew who will be tested before arrival into San Francisco.
“There are fewer than 100 guests and crew identified for testing, including all in-transit guests (guests who were on the previous Mexico voyage and remained onboard for the current Hawaii voyage), those guests and crew who have experienced influenza-like illness symptoms on this voyage, and guests currently under care for respiratory illness.”