WA Premier Mark McGowan says there are now eight crew members on board a cargo ship which has docked at Fremantle Port who are suspected of having COVID-19.
The BBC California, which departed Indonesia last week, has 14 crew members aboard.
Mr McGowan said eight crew members left the vessel briefly so they could have COVID swabs taken, before returning to the ship.
The results of their tests are expected to be known later today.
"Every precaution is being taken to ensure the safety of port workers and the WA community," Mr McGowan said.
"It's essential we don't allow our hard work to be undone."
The vessel was originally scheduled to berth at Kwinana where it was to be loaded with ammonium nitrate, before heading to the port of Newcastle, in New South Wales.
Some of the crew members had been unwell since July 12, Mr McGowan said, and were therefore at risk of sudden deterioration.
He said if the eight with symptoms tested positive, the rest of the crew would also be tested.
On Sunday Premier Mark McGowan said the ship's captain had requested the crew be medically assessed given their symptoms.
"We are assuming COVID-19 is on board this ship, so every precaution will be taken," he told reporters.
"We need to do everything we can to reduce the risk to our community.
"I would have liked this ship to return immediately to Indonesia, but this wasn't possible considering the number of ill crew members on board."
Crew members could receive hospital treatment
Mr McGowan said his preference was for all crew members to stay on board the ship.
But Mr McGowan said he expected that if anyone was so unwell they had to come off the ship they would go into hospital.
"We will do everything we can to keep the crew members on board to make sure they are managed on board in individual cabins, medically assessed," he said on Sunday.
"If anyone needs to be taken off and put into isolation in a hospital and managed that way, then that is what will occur.
"If the crew members and the ship becomes operational again we expect it to leave as soon as it possibly can."
He said the situation with this ship was more difficult, because this crew appeared "so heavily infected".
Earlier this month a bulk carrier was turned away from WA after a crew member in his 50s was brought ashore and taken to hospital with COVID-19.
Mr McGowan said that crew member was still in hospital, and is currently the only COVID patient in hospital in WA.
