NSW Health Minister Brad Hazzard has blasted criticism of the Government's handling of the Ruby Princess issue, following fresh revelations that health authorities had been given specific reports about ill passengers.

Key points: Thirty-six people presented to the Ruby Princess's clinic with flu-like symptoms, NSW Health said

Thirty-six people presented to the Ruby Princess's clinic with flu-like symptoms, NSW Health said The numbers "fell short" of an outbreak, the health authority said

The numbers "fell short" of an outbreak, the health authority said Seven people have died and at least 600 confirmed cases nationally have been linked to the ship

In a heated press conference on Saturday, Mr Hazzard and NSW Chief Medical Officer Kerry Chant faced tough questions over the decision to let the cruise ship passengers disembark in Sydney on March 19.

Dr Chant defended the actions of NSW Health based on the information given to them at the time, which was deemed low risk.

"Hindsight is a great thing and all I can say is, as the minister indicated, a team of professionals considered the information," she said.

"I think it is clear that the influenza outbreak on the ship or the influenza activity on the ship … did leave them to conclude that the respiratory illness [cases on board] was due to influenza activity.

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She said it was now clear patients who left the ship had COVID-19.

"In retrospect … we could all we wiser," Dr Chant said.

NSW Health has said it knew of 104 "acute respiratory infections" on the ship, of which 36 people had "influenza-like illness" before giving the passengers the green light to leave.

It has been confirmed that leaked emails between the ship's doctor and NSW Health showed the health department authorised disembarkation despite being told the ship had collected samples from 15 passengers for flu symptoms.

In the emails, NSW Health advised the samples were submitted for COVID-19 testing and all disembarking passengers were to self-isolate for 14 days, reports said.

NSW Health, however, said the "numbers fell short of the definition of an 'outbreak'," and the ship was assessed as low risk.

Mr Hazzard said it was a time to support health staff working in difficult conditions.

"Today, when I read some of the headlines, I have to say my heart went out to those senior health staff [involved]," he said.

"I find it disappointing, in the strongest way possible, that there can be any suggestion that those people are not doing their best."

He said senior staff were working long hours and those public health doctors making assessments on the cruise ships that come through Sydney very year were "among the world's best".

He said people should take a step back and "be very temperate and careful" in any criticism of health staff.

A cordoned off area on the Ruby Princess. ( Supplied )

'Could not have been prevented'

The ship, which docked in Sydney on March 19, had 2,647 passengers and 1,148 crew.

It remains off the NSW coast as the quarantine period covering its crew continues.

There have been 342 confirmed cases from passengers in NSW alone, with an additional 11 confirmed cases of community transmission.

Nine crew members have also tested positive.

Seven people have died, and the total national number of cases linked to the ship is at more than 600.

Dr Chant said they believed the reason case numbers grew so quickly was because some crew members working in the food preparation galley were unwell which "would have led to a significant risk of transmission".

In the statement, NSW Health defended its position.

"Transmission of COVID-19 amongst these passengers could not have been prevented by NSW Health staff," it said.

"No cases of COVID-19 were identified on board the ship before it docked.

"The vast majority of these passengers reported they did not develop symptoms until after leaving the Ruby Princess."

It added that risk was balanced against passengers self-isolating at home against remaining on the ship facing a rapid spread of the virus.

A war of words broke out between federal and state authorities last month over who was to blame.

NSW Premier Gladys Berejiklian has tasked Police Commissioner Mick Fuller with investigating the circumstances surrounding passengers being granted the green light.

Opposition Leader Jodie McKay said Ms Berejiklian needed to be held accountable.

"The Premier is front and centre in that cover-up," Ms McKay said.

"She must take responsibility and she must apologise.

"The Premier has blamed the captain of the ship and Border Force, but all along it was NSW Health that allowed those passengers to disembark without being tested."

Meanwhile, Shine Lawyers is launching a class action against the owners and operators of the Ruby Princess, Carnival Cruises, for what it says are breaches of the law associated with the liner embarking passengers when there were potential risks.

"We have spoken to dozens of passengers on the cruise so far and they have told us a common story about the fact that they were given no warnings whatsoever about the real substantial risk that they faced," the firm's practice leader of class actions Vicky Antzoulatos said.

It expects the number of passengers joining the class action to grow.