Health officials were advised by police of the arrivals on Saturday and say they have been taken into hotel quarantine for 14 days.

All travelled through Sydney and were identified as soon as they arrived at Perth Airport.

Under the trans-Tasman travel bubble, anyone arriving from New Zealand is currently restricted to NSW and the Northern Territory.

WA Premier Mark McGowan said the situation was not ideal.

"We would prefer better management of these arrangements but this is something that happened that was outside of our control," he said.

The premier initially said 25 people had travelled to Perth through the NZ bubble arrangement but that figure was later revised to 23 by police.

Meanwhile, another COVID-19 case has been confirmed in an international worker who remains in hotel quarantine.

It comes after two cases were identified in crew members on two bulk carriers, one docked at Geraldton and one docked in Fremantle.

The case on the Key Integrity in Geraldton remains on board the ship while the case linked to the AL Messilah has gone into quarantine after initially being admitted to Fiona Stanley Hospital.

"Management plans for both vessels will be determined with the shipping owners, shipping agents, port authorities and the Australian Maritime Safety Authority," health officials said on Sunday.

"The Department of Health continues to interview personnel who boarded the AL Messilah as per operational requirements for a livestock vessel prior to the positive case being confirmed.

"Ongoing contact tracing also continues related to the charter bus transfer and treatment at Fiona Stanley Hospital."

The new case on Sunday takes the total diagnosed in WA since the start of the pandemic to 714.

Twenty of those are still considered active.

Australian Associated Press