The BBC California left Egypt on June 8 and has since visited three ports in Indonesia.

Seven of the 14 crew members aboard became unwell on or about July 12 and the captain has asked for the crew to be medically assessed.

West Australian Premier Mark McGowan says the ship will be able to berth in Fremantle only for medical assessment and a special medical team will go on board.

"We are assuming COVID-19 is on board this ship, so every precaution will be taken," he told media on Sunday.

The sick crew members are six Filipinos and one Russian, with the rest of the crew from Bulgaria, the Ukraine and Russia.

They are isolating in separate cabins and do not currently require medical help.

But Mr McGowan said there was a risk of a sudden deterioration in their health, which could lead to a maritime emergency.

"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," he said.

"If all the crew get sick and can't operate the ship, can't function out on the high seas ... who knows what could happen."

He said Western Australia had successfully dealt with about 10 similar situations since the start of the pandemic.

"We cannot allow the virus in through international shipping," Mr McGowan said.

The BBC California operates under the flag of Antigua and Barbuda and was due to arrive on Saturday morning AWST.

WA recorded no new COVID-19 cases overnight.

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

Australian Associated Press