West Australian Premier Mark McGowan says a cargo ship carrying seven crew members with suspected COVID-19 symptoms is set to dock in Fremantle today or tomorrow.

There are 14 crew members aboard the BBC California, with half displaying "COVID-19-like symptoms".

The ship's captain has requested the ill crew members be medically reviewed when the vessel berths in Fremantle, which Mr McGowan said was expected at "some point today or tomorrow". 

The BBC California, which is sailing under the flag of Antigua and Barbuda, departed Egypt in June and has most recently visited three ports in Indonesia.

It departed Indonesia on July 11 and was 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.

"We are assuming COVID-19 is on board this ship," he said.

"I have urged our authorities to ensure everything is done to follow the very strictest health protocols.

"If an outbreak of COVID-19 is detected on board pending further assessment of conditions on board the ship, our teams will manage the situation as best they can.

Mr McGowan said it was assumed that any crew members who were confirmed COVID-19 positive would have the Delta strain.

"Every case we get seems to be the Delta strain [these days]", he said.

Aim is to keep crew members on board, Premier says

The seven crew members were all isolating in cabins, the Premier added.

"We'll do everything we can to keep the crew members on board [and] to make sure they're managed on board," Mr McGowan said. 

"If anyone needs to be taken off and put into isolation in a hospital, well then that's what will occur."

Mr McGowan said the state government observed strict protocols when it came to international vessels, due to the risk they presented to the community. 

"Ports and shipping contribute significantly to our local community and as the engine room to the [national economy]," he said. 

"[But] we can't take any chances or get complacent.

"We cannot allow any risk of the virus entering Western Australia through international shipping."

However, Mr McGowan said the situation was different compared to previous ship infections, given half of the crew were showing symptoms. 

"The risk is the remaining seven crew members might get unwell," he said. 

"[I]f all the crew get sick and can't operate the ship out in the high seas, who knows what would happen ... that is a maritime emergency."

WA recorded no new COVID-19 cases overnight. 

The state has seven active cases, six of whom are in hotel quarantine.

One person, a crew member from the MV Emerald Indah, remains in hospital.

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