The Coral Princess has an undisclosed number of infected passengers and crew as it prepares to arrive in Fremantle on Friday.
Its operator Carnival Australia says most of the ship's 2000 guests are unaffected and those who return a negative rapid antigen test will be allowed ashore.
"We continue to monitor closely a small number of guests who tested positive to COVID-19 and who are isolating and are being cared for in their stateroom by our medical and support staff," Carnival president Marguerite Fitzgerald said.
"All cases on board have been asymptomatic and mildly symptomatic. Case numbers remain relatively steady."
There are also reports of cases being detected aboard the Quantum of the Seas, a ship expected to dock in Brisbane on Tuesday.
The Coral Princess left Broome earlier this week, bypassing a scheduled stop in Geraldton due to bad weather.
WA Health said it was aware of the ship's outbreak but had not been asked for help in managing passengers.
It said all cruise ship operators visiting WA were required to report cases, abide by the national protocols and have their own COVID-19 plans.
People who contract COVID-19 while aboard vessels are advised to isolate for five days.
Large cruise ships have been allowed back in WA waters since October 1 after being banned in 2020.
The NSW government will extend free access to RATs for concession card holders until the end of January.
Card holders can receive up to 10 free RATs over three months.
WEEKLY VIRUS DATA BY JURISDICTION
* NSW: 10,050 new cases, 16 deaths
* Victoria: 8537 new cases, 51 deaths
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