Brits on a cruise ship will have to stay onboard the vessel until they can be flown back to the UK.
At least 33 people from the UK are on board the Vasco da Gama, which is due to arrive in the port city of Fremantle in Western Australia on Friday.
They have been put in quarantine on the ship and will have to remain on board indefinitely.
About 800 of the 950 passengers are Australian and will be taken to nearby Rottnest Island for a 14-day quarantine period, Western Australian Premier Mark McGowan told reporters.
The Britons on the ship will stay aboard until they can be flown directly back to the UK, he told the Australian Broadcasting Corporation.
He said: "All crew and foreign nationals will remain on the ship until arrangements are made to fly them directly out of the country.
"They will not be allowed to disembark at any time, unless it is to travel under strict supervision, directly to the airport, or they need urgent medical attention to survive."
A spokesman for the UK's Foreign and Commonwealth Office said: "We are doing all we can to help British people on board the Vasco de Gama cruise ship.
"Our staff are in close contact with the cruise operator and the authorities in the region to ensure British people can get home safely."
The ship's owner Cruise & Maritime Voyages told The Australian newspaper it had recorded no health concerns among its passengers or crew.
The owner also said no-one has left the vessel since March 14, though some Australian and New Zealanders joined the da Gama on March 18 from Columbus, another of the company's ships.
ABC reported two other cruise ships are being prevented from docking at Fremantle, about 14 miles south-west of state capital Perth.
Mr McGowan said the Artania and the Magnifica are anchored offshore.
About 25 passengers and crew of the Artania have reported respiratory symptoms, and Mr McGowan added one passenger no longer aboard had tested positive for Covid-19 after disembarking.
