Sydney, Apr 14 (IANS): A criminal investigation into a cruise ship which disembarked COVID-19 infected passengers into Sydney could take up to six months, officials revealed on Tuesday, while the departure date of the ship from Australian waters remained unclear.

"What was initially regarded as a couple of months work will now be in total six months, but we are now a month into it, so it will be around five months," New South Wales (NSW) State Premier Gladys Berejiklian said.

The Ruby Princess, which docked in Sydney last month, has been linked to over 600 confirmed COVID-19 cases within Australia and at least 18 deaths, reports Xinhua news agency.

It was subsequently moved to a port south of the city to undergo testing and treatment of infected crew members still onboard.

The probe would look at what the ship's operator Carnival Cruises knew about COVID-19 infection on board before thousands of passengers disembarked in Sydney on March 19.

All of the 2,647 passengers as well as more than 1,000 crew members from more than 50 countries could potentially be interviewed by police as part of the criminal investigation.

NSW Police Commissioner Mick Fuller said on Tuesday he could not confirm when the ship would leave Australian waters until medical officials give notice regarding the health of crew members.

"It is not docked indefinitely, we do need to reach a point where NSW Health are satisfied that we have passed the transmission rate, that we can send the ship on its way without endangering anyone's life," Fuller said.

NSW Health said on Tuesday that 128 crew members on board had tested positive to COVID-19 with 59 of them no longer showing symptoms.

Australia has so far reported 6,494 confirmed coronavirus cases with 61 deaths.