The Coral Princess has an undisclosed number of virus cases among passengers and crew, although the operator, Carnival Australia, says most of its 2000 guests are unaffected.

The ship left Broome for Geraldton earlier this week, but bad weather forced it to bypass its scheduled stop there on Thursday and head straight to Fremantle.

Carnival Australia said the change of schedule was on the advice of the Mid West Ports Authority.

In a statement, the authority said wind and swell forecasts were outside the usual safety parameters for what would have been the largest and longest ship to berth in Geraldton.

"Understandably, larger vessels have smaller tolerances and pose greater safety concerns," it said.

"Weather conditions are a contributing factor when assessing safe operational parameters, and in this case the conditions are outside of these parameters."

The City of Geraldton said the community had been excited about the return of cruise ships, and the decision on the Coral Princess "isn't the news we wanted to hear".

"We hope to welcome her back in the future,'' a spokesman said.

The liner is now expected to dock in Fremantle on Friday, with passengers who return a negative rapid antigen test to be allowed to go 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 Australia said in a statement.

"All cases on board have been asymptomatic and mildly symptomatic.

"Case numbers remain relatively steady."

This week, WA Health said it had been advised of the virus cases on the liner, but said it had not been asked for help in managing those impacted.

It said all cruise ship operators visiting WA must abide by the national protocols and have their own COVID-19 plans.

"In accordance with the protocols, while in WA waters cruise operators should report COVID-19 cases to WA Health 12 to 24 hours prior to arrival in a WA port," it said.

"The protocols set out the minimum standards expected, which include the need for reporting to occur.

"Those on board vessels who have COVID should isolate for five days."

Large cruise ships were banned from WA waters in 2020.

The ban was lifted in April for ships with up to 350 passengers.

Larger ships were allowed to return from October 1, with the Coral Princess the first to visit the region.

Australian Associated Press