A second cruise ship is being held off the coast of California, raising fears more Australians are stranded in their cabins as US President Donald Trump's administration attempts to curb the spread of coronavirus.
Gold Coast dancer Kylie Chappell and three other Australians are already stuck on the Grand Princess with more than 3,500 other passengers and crew.
Australian consular officials in San Francisco stand ready to provide assistance to the Australians.
US Vice President Mike Pence confirmed on Saturday a second cruise ship is being held off California after it was discovered crew members from the coronavirus hit Diamond Princess in Japan and the Grand Princess may be on it.
"We are tracking at this point a ship that may have shared crew with the Diamond Princess or the Grand Princess and we have taken decisive action to hold until we do a full medical assessment of the crew on that ship," Mr Pence, after meeting with cruise ship executives in Florida, told reporters.
The vice president did not identify the ship being tracked. In an ominous sign, initial tests of just 46 on the Grand Princess found 19 crew and two passengers had the virus.
Mr Trump said on Friday he would prefer the Grand Princess's passengers and crew remain out at sea rather than be allowed to dock on the US mainland.
This is despite the virus spreading on the Diamond Princess when it was quarantined off Japan in February.
The Grand Princess is expected to be allowed to dock at a non-commercial US west coast port and the passengers and crew will be tested and "quarantined as appropriate", Mr Pence said.
"The Department of Foreign Affairs and Trade has confirmed that four Australians are on board the Grand Princess cruise ship," DFAT said in a statement.
"US authorities are testing every person on board, and we are awaiting advice as to whether any of the Australians have contracted COVID-19.
"The Australian Consulate-General in San Francisco stands ready to provide consular assistance, in accordance with the Consular Services Charter, to any Australian citizen aboard the vessel, should they require it."
Ms Chappell, who travels the world performing on cruise liners, is one of 1,111 crew on the Grand Princess.
Fears grew the Grand Princess could be carrying coronavirus when passengers on the ship's previous voyage to Mexico were diagnosed and one, a 71-year-old from California, died.
Passengers on the current Grand Princess cruise, which was returning to San Francisco after a trip to Hawaii, have been quarantined in their rooms since Thursday.
They have meals delivered to their rooms.
Daniel Healy, 56, told the San Francisco Chronicle he and his wife were trapped in their room like "mushrooms kept in the dark" and he ran out of diabetes medication on Friday.
Australian Associated Press