Counsel assisting the inquiry Richard Beasley SC believes the commission should find there was an unreasonable wait for results after the swabs were taken from the ship in the early hours of March 19.

In closing submissions on Wednesday, Mr Beasley said it was unacceptable the results weren't known to NSW Health until 10am on March 20, after passengers on the virus-affected ship had already disembarked.

"Whether or not the risk is assessed as low, medium, high or catastrophically high or unbelievably low, these samples should have been tested immediately," he told the inquiry.

"I know that might have meant an early morning for someone in a lab, but in a pandemic that might be part of the job.

"It was important to know as soon as possible whether or not COVID was circulating on the ship. The swabs weren't taken for fun."

NSW Health argued the time taken to get results was reasonable in circumstances where the ship had been assessed as low risk.

The Ruby Princess, which docked at Circular Quay on March 19, has since been linked to more than 20 coronavirus deaths across Australia.

Swabs were meant to be taken for COVID-19 testing from everyone with influenza-like illness but the ship didn't have enough swabs available, the inquiry on Wednesday heard.

In his submissions, Mr Beasley said there was an "element of luck" that of the swabs taken off the ship, some did return a positive result and reveal the virus on board.

He said a health assessment panel should have boarded the ship upon its arrival to swab anyone else who was a suspect case.

All passengers should have been confined to their cabins, he added.

"As soon as a positive result was known ... the only practical course then is that all passengers and crew are securely removed from the ship because they are all suspect cases of COVID, and they are taken into what I will just call quarantine," Mr Beasley said.

Counsel assisting also submitted that the medical department of cruise operator the Holland America Group should have realised from March 10 that there were suspect cases on board.

They should have made that clear to the passengers and crew so they could make decisions about how they looked after their own health on board, the inquiry heard.

"I know that's a difficult decision, no doubt, to make in relation to a cruise where everyone's meant to be having a holiday and fun," Mr Beasley said.

"But once there (are) suspect cases of COVID on board, in my view there was a very clear obligation: to make passengers and crew aware of that."

Counsel assisting noted at the start of Wednesday's hearing that an expert report to the commission considered that the coronavirus public health response in NSW and Australia had generally been exemplary.

"It's early days in the pandemic still but that is, in part, a matter for context," Mr Beasley said.

The inquiry continues.

Australian Associated Press