A coronavirus cluster was detected Tuesday on a freight ship berthed in the Australian west coast port of Fremantle, raising questions about why local authorities weren't alerted to the danger.

Six of the 48 crew members from the Al Kuwait tested positive for the virus four days after the livestock carrier arrived from the United Arab Emirates on Friday, Western Australia state Premier Mark McGowan said.

The six infected crew were transferred to hotel quarantine in the nearby city of Perth while health officials consider what to do with the remaining 42 on board, he said.

The ship's cargo of 56,000 sheep is being held at a feedlot near the port. They were to be loaded within days and cannot be returned to farms because of quarantine restrictions, McGowan said.

Authorities expect more crew members will get sick and the ship will need a deep cleaning before it can leave.