NSW Police Commissioner Mick Fuller has revealed there are nine cruise ships either docked in NSW or waiting off the coast, as authorities implored all to sail to their home ports immediately rather than risk flooding the state's hospitals with coronavirus patients.

"All the hard work we've done could be over. We will continue to allow them to have fuel and food ... but it is time to go to your port of origin," Mr Fuller said.

Carnival Australia, however, says it is not safe for the ship to sail away from Australia while there are ill crew members on board.

"While illness on board has been reduced due to strong health management, the ship needs to remain within reach of Australia to access healthcare services if an urgent need arises," the company said in a statement.

Six seriously ill crew members have already been transferred to NSW hospitals.

Carnival said it is currently "in high-level federal and state discussions with the aim of enabling the repatriation on compassionate and humanitarian grounds".

There are 1100 crew on the Ruby Princess from 51 countries. The company argues while the ship is registered in Bermuda, its home port is effectively Sydney given it was here on a six-month cruise season.

The Ruby Princess has become a major source of COVID-19 cases in Australia after infected passengers were allowed to disembark without adequate checks.

There are 324 coronavirus infections in NSW linked to cruise ships, including 211 cases from the Ruby Princess and 79 from the Ovation of the Seas.

Australian Associated Press