A crew member on board a ship docked at Kwinana has tested positive to COVID-19.
The man, aged in his 20s, presented to Fiona Stanley Hospital for an unrelated illness on Sunday and had no COVID-19 symptoms.
"He produced a weak test and was sent back to the ship in isolation whilst further testing was undertaken," Premier Mark McGowan said.
"He was then found to be positive and he's been taken off the ship and put into (hotel) quarantine."
Mr McGowan said the man wore PPE while being transported to the hospital and to the quarantine hotel and health staff followed infection control processes.
"The risk to Western Australia is very low," he said.
There are 22 crew members on the Allegra vessel which was due to leave port at 10pm last night.
Mr McGowan said there is a strong chance more crew members could test positive and he wants the Allegra to leave WA as soon as possible.
The State Government are working with Federal authorities to manage the departure of the Allegra from the Kwinana Bulk Jetty.
18-year-old male from Lakelands charged over incident in Pinjarra
BREAKING: Reports of a man armed with a firearm in the Pinjarra area
Hayden Ballantyne signs with Rockingham Rams
Mayor reassures community that 'no decision has been made' to close 4WD access at Tim's Thicket, White Hills beaches
DBCA 'sick and tired' of illegal access to Port Kennedy Scientific Park
Mandurah homeless camp goes up in flames
Dawesville community shocked after kangaroo deliberately mowed down
Teens armed with knife, scooter charged over Rockingham Shopping Centre fight
Mandurah private school teacher charged with alleged sexual abuse of male student