"The ABF officer made internal enquiries and subsequently advised the NSW Port Authority that the vessel had been cleared by NSW Health,"a statement from Border force said.

"The ABF did not seek to shape or influence any view or decision by the NSW Port Authority."

NSW's total confirmed cases of COVID-19 stands at 2734,an increase of 49 cases on the previous day. There are 227 people being treated by NSW Health,including 36 patients in intensive care and 22 on ventilators.

Premier Gladys Berejiklian told her MPs in a recent party room meeting that Border Force had wrongly told NSW Health that the cruise ship was deemed"low-risk"before it docked on March 19.

Almost 2700 passengers were allowed to disembark in the early hours of March 19,with four cases of coronavirus confirmed hours later.

An MP who was in the party room said Ms Berejiklian"made it very clear that we did not fail,we were not responsible".

"She was very defiant. We were absolutely not to blame,"the MP said.

But her comments prompted the Border Force Commissioner Michael Outram to hit back.

"What broke down in this case was ... health officers,trained doctors or nurses didn't get on board the vessel,swab passengers and take their swabs for results,"Mr Outram said on March 25.

He said his officers were responsible for ensuring there was no contraband and ensuring everyone had visas. The Department of Agriculture had the biosecurity responsibility,Mr Outram said.

NSW Police Commissioner Mick Fullerrevealed on Sunday there would be a criminal investigation,led by homicide detectives,and a likely coronial inquiry.

Mr Fuller said an investigation was critical to determine whether the operators of the ship,Carnival Australia,were"transparent"about ill passengers.

He also singled out the Ports Authority as doing an"exceptional job"after phone logs between the the authority and Carnival Australia suggested the ship downplayed the risk of COVID-19.

The logs show the Ports Authority had initially not allowed the ship to dock because of coronavirus fears but then overturned that decision after being led to believe that there was no virus threat.

On Wednesday,30 detectives from State Crime,Counter Terrorism and Special Tactics and Marine Area commands were seconded to the criminal investigation dubbed Strike Force Bast.

Investigators will interview"high-priority witnesses"this week and are urging passengers with relevant information to contact Crime Stoppers.

Ms Berejiklian said the investigation would not be a drawn-out process.