Eight crew members aboard a cargo ship docked in Fremantle have tested positive to COVID-19, creating a fresh logistical challenge for West Australian authorities.
WA's health department has confirmed the results after the symptomatic crew members briefly disembarked the BBC California vessel for testing earlier on Monday.
They have since been isolating in separate cabins aboard the ship.
"The remaining six crew on-board the vessel, who are not symptomatic, will now be tested for COVID-19 this afternoon," WA Health said in a statement.
"They will also receive serology tests to see if they have previously had the virus.
"Every precaution is being taken to ensure the safety of port workers and the WA community."
Premier Mark McGowan had earlier flagged the strong likelihood of positive cases among the crew.
He said anyone who needed medical treatment would be hospitalised, but doing so would increase the risk of community infection.
"If the crew can remain on board the ship and they can quarantine there, it reduces the risk to all of us," he told reporters.
The BBC California left Egypt on June 8 and has since visited three ports in Indonesia. A number of crew members became unwell last week, prompting the ship's captain to seek assistance.
The ship docked at Fremantle Port on Monday, allowing crew members to disembark in small groups so they could be tested inside a shed.
They were met by health workers and police, clad in personal protective equipment, and returned to the ship a short time later.
WA Health said the same process would be followed for the remaining crew members and further medical assistance would be provided if required.
The crew includes six Filipinos, with the rest from Bulgaria, the Ukraine and Russia.
Mr McGowan said WA had successfully dealt with about 10 similar situations since the start of the pandemic.
"If we had tried to force the ship to sail with a crew that is entirely infected and the crew couldn't operate the ship, that's an emergency at sea," he said.
"That have could have had all sorts of catastrophic consequences for us, as well as the people on board."
WA recorded one new COVID-19 case on Monday, with a woman in her late teens testing positive upon returning from overseas.
The state has seven active cases.
Authorities are closely monitoring the situation in South Australia, which has imposed widespread restrictions after detecting two new local cases.
WA has a hard border in place for NSW, Victoria and Queensland, but SA travellers currently do not have to quarantine unless they have been to exposure sites.
"It doesn't necessitate a change to the rules at this point in time, but if we have to, obviously we will," Mr McGowan said.
"You'd have to say of all the states in Australia, we've been the toughest on all these sorts of things to try and keep the virus out and our measures have largely worked."