The massive criminal investigation into a deadly outbreak of coronavirus in Australia stemming from the Ruby Princess cruise ship is expected to be finished by September this year.

Key points: The ship is still docked at Port Kembla, south of Sydney

The ship is still docked at Port Kembla, south of Sydney Police are working with its operator to provide medical support for sick crew

Police are working with its operator to provide medical support for sick crew Eighteen deaths and more than 600 coronavirus cases have been linked to the ship

NSW homicide detectives may have to interview all of the 2,647 passengers on the ship as well as more than 1,000 crew members from more than 50 countries.

"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," Premier Gladys Berejiklian said.

The investigation will look at what the ship's operator Carnival Cruises knew about potential COVID-19 cases before thousands of passengers were allowed to disembark in Sydney on March 19.

Eighteen coronavirus deaths, and more than 600 cases, have been linked to the ship.

Ms Berejiklian will seek legal advice this week on whether a Special Commission of Inquiry could run alongside the homicide investigation.

In NSW, a Special Commission of Inquiry is launched when the Premier appoints a prominent current or former legal professional to probe an issue.

"We will have to get legal advice first to make sure anything we did did not compromise what the police are doing or what the coroner would do," she said.

"We will not be leaving a single stone unturned, let me assure the community of that.

"All of us want to know what went wrong, all of us want to make sure this never happens again."

Police Commissioner Mick Fuller said Crime Stoppers had been inundated with hundreds calls with information about the ill-fated cruise ship.

"If the matter finishes and the state coroner decides not to have an inquest then I am happy to release all the information and the findings," he said.

"I can't push a criminal investigation to go faster than what is ethically possible."

Authorities have been unable to say when the Ruby Princess will be allowed to leave Port Kembla, south of Sydney.

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

Commissioner Fuller will meet with health officials today to discuss when the Ruby Princess can leave Australian waters.

Once NSW Heath deems it safe, the ABC understands police will be able to order Border Force officials to assist with the ship's departure.

Staff from private healthcare provider Aspen Medical will continue to assist crew members who have reported flu-like symptoms on board the ship.

"We are working with Carnival and the ship to make sure anyone who is ill is brought off the ship and is treated properly," Commissioner Fuller said.

At least 88 crew members have been tested on board, with 66 returning positive COVID-19 swabs.