A Ministry of Health statement confirmed the additional cases this morning after test results for the crew members were received late last night.
Yesterday two cases were revealed after rapid testing on symptomatic crew members came back positive.
The nine positive cases come from a total crew of 21 people.
The Mattina is quarantined in an area of the port inaccessible to the public, with additional fencing being erected to further restrict public access to the area.
No crew members have come ashore, and the only South Port employee to board the vessel was a harbour pilot who boarded the ship to guide it into port.
It is mandatory for a pilot to board a ship of this size when berthing, and the pilot in this case was fully vaccinated and wearing personal protective equipment (PPE).
South Port said in a statement all crew members remain on board the Mattina which is quarantined in a secure area of the port which is inaccessible to the public.
Fencing has been erected to further restrict access to the ship.