Dozens of passengers and crew onboard the the Artania cruise ship in Fremantle have likely been infected with coronavirus and will be treated at private hospitals in Perth.
Premier Mark McGowan said the Commonwealth had contracted Bethesda and Hollywood hospitals to treat the foreigners.
"Cruise ships continue to be the Achilles heel when it comes to managing this situation," he told reporters on Saturday.
"I'm pleased so say the Commonwealth agrees this matter is their responsibility."
Mr McGowan said the Artania hit a crisis point on Friday night when it was revealed 77 people had virus-type symptoms and another person was evacuated for a separate illness.
WA health experts went aboard on Saturday, concluding 46 people should be tested for coronavirus, including 30 passengers and 16 crew.
Anyone who tests positive will be treated at the private hospitals.
Seven of the nine people who disembarked on Friday, who tested positive, will no longer be quarantined at the WA police academy, and will instead go to the hospitals.
Two other people were previously evacuated from the ship for other medical reasons, then subsequently diagnosed with COVID-19 and remain in a critical condition.
Health minister Roger Cook said it was likely the third emergency evacuee would also test positive.
Mr McGowan said four chartered flights would take about 800 healthy passengers and some crew back to Europe.
New Zealanders onboard the Vasco da Gama cruise ship, which is also docked in Fremantle, will be assessed before flying out on Saturday evening.
There are also about 30 British people onboard.
About 200 passengers from WA will soon go into isolation on Rottnest Island for 14 days, while about 600 other Australians will quarantine in WA for two weeks before heading home.
Cruise ship Magnifica, which is anchored off Fremantle, is reprovisioning and will leave later on Saturday.
A fourth ship, which only has crew onboard, also needs to reprovision and refuel.
"The truth is that there's no perfect solutions in this whole set of events," Mr McGowan said.
"We don't want passengers from cruise ships wandering around the streets."
WA has 23 new cases, including the confirmed Artania passengers, taking the state's total to 278.
There are 14 people in hospital, including six in intensive care.
Mr Cook said the overall numbers were "very encouraging".
"What this means is that we are continuing to identify all the people who are at risk of contracting COVID-19 and we are isolating those people," he said.
Australian Medical Association WA president Andrew Miller said a lockdown was inevitable.
"The sooner we do it, the more effective it is and hopefully the shorter it will be."
But Mr McGowan said he did not like the term "lockdown".
"We need to be careful in our language ... there may well be further changes, but if there are, we will announce them in coming days, and if those changes are put in place it's for the common good."
A 61-year-old man on his way to the beach has been charged after allegedly failing to comply with a direction to self-isolate upon his return to WA from Indonesia last week.
Australian Associated Press