Eight crew on-board a cargo ship docked in Perth have tested positive for Covid-19, sparking fears for the other six people on the vessel.

Health officials and police were at Fremantle Port about 9am on Monday to assist the crew members suffering coronavirus symptoms to disembark the BBC California for testing. They then returned to the vessel.

Later that afternoon, the Health Department confirmed they had all been diagnosed with Covid-19 following rapid PCR testing.

“The crew and shipping agent have now been informed,” the Health Department said in a statement.

The remaining six crew on-board the vessel, who are not symptomatic, will be tested later on Monday and will then immediately return to the ship.

They will also receive serology tests to determine whether they had previously contracted the virus.

“For now, the vessel will remain berthed at Fremantle Port, with all crew members remaining on-board,” the department said.

“However, medical assistance will be provided to crew if required.”

Earlier, Premier Mark McGowan told reporters the pilot who brought the ship in was wearing full personal protective equipment.

“Those eight symptomatic crew members were taken off the ship temporarily, all wearing masks, gloves and observing safe distancing. They were taken into a purpose-made swabbing station,” he said.

“The crew then returned to the ship to continue to isolate in their cabins.”

Mr McGowan said every precaution was being taken to ensure the safety of port workers and the West Australian community.

“No health staff boarded the ship. Land-based port workers wore the required PPE, including gloves and masks, and followed all approved processes,” he said.

“Our authorities are working closely with the captain, shipping agent, vessel owner and the Commonwealth agencies to manage the ship and the crew.”

The ship departed Egypt last month, then travelled to ports in Indonesia before reaching WA waters.

Crew members are believed to be from the Philippines, Russia, Ukraine and Bulgaria.

Mr McGowan said it appeared to be a “heavily infected” ship, which made it more difficult for authorities, but he was advised they all had separate cabins.

“Obviously, if the crew can remain on-board the ship (and) they can quarantine there, it reduces the risk to all of us,” he said.

“If you take the crew off the ship and then transport them around the place, and take them to hospitals and airports … it actually increases the risks.”

WA recorded one new virus case overnight in hotel quarantine — a woman in her late teens.

Seven active cases remain in WA, including one man who is in a stable condition in hospital.

He became ill on-board another ship — the Emerald Indah — and was taken off the vessel in Geraldton.

Meanwhile, WA Health Minister Roger Cook said the state’s contact tracers had “swung into action” to help New South Wales with its outbreak.

“Over the weekend, we did contact tracing for 31 cases,” he said.

“The cases were very complex, in large families. Some 18 of these cases require the assistance of an interpreter.”

Seventeen staff were dedicated to NSW contact tracing on Saturday, assisting with 20 cases, while a further 16 staff helped with 11 cases in Sunday.

“The NSW situation is obviously of extreme concern and still evolving, so I would expect our team to be helping out for as long as is required,” Mr Cook said.

Mr McGowan said his thoughts were with everyone in NSW and Victoria.

He again urged people in those states to follow the lockdown rules to “crush and kill” the virus.