NSW Premier Gladys Berejiklian and Chief Health Officer Dr Kerry Chant have been grilled about the state's handling of the Ruby Princess' arrival in Sydney.

Thousands of passengers were allowed to disembark from the cruise ship last week despite several people being tested for coronavirus.

Here's what they said at today's press conference:

Reporter: Premier, it seems that the Ruby Princess issue has been a significant source [of coronavirus cases]. Is Border Force to blame for this?

Premier: Every single agency needs to take responsibility for our borders. Whether it's a ship at a port, whether it's a plane load of people coming in from overseas. We're still having thousands of people coming in on planes every single day.

All authorities have to step up, including NSW Health, including all the other authorities involved.

What is really imperative at this time, we realised, is strong communication between authorities and everybody stepping up.

This a joint responsibility for all of us, whether you're the traveller, a federal authority or a state authority and it's really important for all of us to adhere to what we need to do.

I'm pleased that everybody is working closer together, because the number one priority for us is to make sure we contain the disease, that we control the spread.

And we know from the statistics and we know from what's occurred since Australia Day really, the vast majority of cases to date are from people who come from overseas, and we want it to stay that way.

As Dr Chant said, many nations around the world have higher rates than Australia and NSW do and, unfortunately, many people who are coming in via planes or other modes of transport have acquired the disease.

We know that and that's why we're ramping up not just what we do at the borders, but also what we do once those people self-isolate because the vast majority are doing the right thing, but unfortunately Crime Stoppers had a number of calls increasing day-by-day from people who are rightly dobbing on people who should be self-isolating. I want to thank the police for providing that opportunity through Crime Stoppers.

People need to know that this is not a joke, you need to take it seriously, lives depend on it.

If you need to self-isolate, or a contact of yours needs to self-isolate as a result of the contact they had with you, you need to adhere to the rules because otherwise can be an issue of life and death.

Reporter: People are starting to die now as a result of the decision from a bureaucrat somewhere. Surely Australians, NSW people, need to know who is responsible. It's not good enough now to just share that blame. Who was responsible, who will take responsibility and will there be consequences, will someone lose their job?

Premier: All of us have to take responsibility. But [Dr Kerry Chant, NSW Chief Medical Officer] wants to comment so I'll let her comment.

Dr Kerry Chant: Let's be very clear about the circumstance because I think it is very important that the community understands.

We recognised the COVID-19 was on the ship and we have followed up all of the passengers on the ship.

Those passengers that are recognising symptoms had been infected on the ship and no action by NSW Health or otherwise could alter that.

So everyone who has presented symptoms — including the 77-year-old who tragically died — was taken from the ship to the hospital.

So there's no issue that could have been prevented by any action.

All of the people from the ship were asked to self-isolate and that is because they had come from New Zealand.

New Zealand had actually undertaken testing for COVID-19 on the ship and there had been no evidence of the virus.

Also, when we follow-upped a number of the passengers on the ship, they developed symptoms on the day of departure.

The boat came in at 6:00am that morning and their reported symptom onset was, for the vast majority, either that day or subsequent days.

So what we saw was clearly seeding and we are particularly concerned that a crew member on board that ship had the disease and then potentially that person may have contributed to the spread.

We're doing a thorough investigation but please be assured that these passengers were asked to self-isolate.

We follow-up all of the contacts of these passengers and as soon as we have a confirmed case, we ring-fence those cases — many of which are still the Ruby Princess passengers who themselves are close contacts, in order to prevent any further spread.

The cases we are reporting occurred and were exposed on the ship.

There is no action that NSW Health could have taken to prevent those people acquiring the disease.

What we are working to immediately identify is any onward transmission from any contact from those people travelling home.

Now, if symptoms developed in the returning passengers days after they departed, they were then non-infectious when they were travelling home. These are all under investigation.

We're taking this matter very seriously and we're doing all we can to make sure that any further contacts of those contacts are again locked down.

So the community should be reassured that through those actions, albeit if we had of known this, we would have acted in a very different way, that there is no minimised spread into the community.

Reporter: The Carnival Cruises, that crew member, have they lied to the people?

Dr Chant: The crew member wouldn't have known. There was no recognition that anyone on that ship had COVID-19.

The reports of the level of activity and respiratory virus activity on that ship didn't indicate any pattern of it.

What's evident from the graph when we're doing the epidemiological investigation is that there was an upswing in cases when this cruise ship deboarded and disembarked at 6:00 in the morning.

A lot of people had mild symptoms onset on the day they got off that cruise ship.

We will be releasing a report on the cruise ship so we're transparent to the community, but to be perfectly frank, our focus has been rapidly diagnosing cases amongst the cruise ship arrivals and also making sure that we identify any people who would have been in contact with those cases in order to close down any transmission in the community.

So, I want to be clear, those cases we're reporting now were exposed on the cruise ship.

There is no action that New South Wales Health would have — could have taken to stop those cases.

Our focus now is identifying whether there is any evidence on board transmission from those people who have had symptom onset on the day of the cruise or the day after because we take people's infectious period as 24 hours before symptom onset. That work is our key priority and we're working with any states and territories to also follow-up passengers.

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Reporter: When you think they were exposed on the cruise ship. When the ship came in on 8 March, 18 people, nine crew and nine passengers were tested for COVID-19, came back negative. So should you have tested more - New South Wales Health tested more people?

Dr Chant: I think you're talking about a previous journey of the Ruby Princess, is that what you're...

Reporter: Yes, previous journey

Dr Chant: We actually did — so this goes to the risk assessment process we undertake. So on a previous cruise ship for the Ruby Princess there was an indication that there was an outbreak on board the ship so that was investigated.

Health teams that elevated the risk from a low risk scenario to a medium risk.

We actually deployed teams to the cruise ship and undertook testing and excluded them. So our process was based on the best available information.

Of course we would have responded differently if we had of known.

I wanted to reassure the community that we had extensive planning underway. We had food packages ready to provide food to passengers, we had health share on stand-by.

We had don contingency planning. We had where we would accommodate people in hotels.

So people be assured this was not an intention of NSW Health in conjunction with our Border Force to allow this cruise ship to disembark passengers with known COVID. This is not the case.

Reporter: But three passengers came off on stretchers and put in ambulances.

Dr Chant: My understanding there was one passenger who was transported to Royal Prince Alfred Hospital and I can follow-up what the other two passengers — I'm not aware of the details.

Reporter: But if people are coming off in ambulances and stretchers, surely alarm bells should have gone off and the whole system should have said, "stop".

I will go back to what was known at a particular point in time, but it is not unexpected that from time to time cruise ships do disembark [ill] passengers.

I will look at what information was available to them. Be assured we are doing a thorough investigation and we'll release the report publicly but I can't highlight enough that many people's symptom's onset occurred on the day of departure noting that disembarkation and subsequent days.

Reporter: The new numbers from today, the increase, are more people linked to the Ruby Princess?

Dr Chant: The Ruby Princess has certainly increased the numbers and contribute significantly to the numbers.

Today I can break it down by the Ruby Princess but clearly I will do that in terms of breaking down the numbers.

But again the fact that this — the passengers on board this ship are self-isolating, the fact we're diagnosed them that we are - the issue for us is really making sure any close contacts of those individuals are also self-isolated and make sure we ring-fence them.

That's the area that we could have prevented transmission. But we could not have prevented the transmission. These people were exposed on the Ruby Princess. The numbers will increase, as I indicated to you.

The incubation period is somewhere in the order of one to 14 days. We will potentially still be seeing people on the Ruby Princess who were exposed on the last day or the some time in that period who may well develop symptoms and that's not as a consequence of anything we could have prevented.

The main focus of us in terms of any onward risk is anyone who's been contacts of those people on the Ruby Princess.