They came to Sydney for the trip of a lifetime but went home with a deadly souvenir.

And, while much has been written about the swathe of coronavirus infections on the Ruby Princess, about 900 passengers dropped off the radar.

Key points: The ABC has spoken to Canadian travellers on the Ruby Princess

The ABC has spoken to Canadian travellers on the Ruby Princess They said the company "could not have done more to put our health at risk"

They said the company "could not have done more to put our health at risk" Princess Cruises said it "followed the federal and state health clearance processes to the letter"

Some 2,647 passengers were travelling on the 13-day return trip from Sydney to New Zealand before it docked two days earlier than planned on March 19, as Australia began to clamp down on cruising in a bid to stop the spread of COVID-19.

About two thirds of the passengers were Australian and among them, 18 have died from the virus and hundreds more have been infected.

But much less is known about the 900 overseas guests — many of whom left the ship and the country without knowing they had been exposed to the bug.

Martine Carrier, 61, who travelled in a group of four Canadians said she thought she'd be safe on the Ruby Princess.

"Boy, was I wrong," she said.

"I am extremely angry at Princess because, contrary to what Princess says, that the passengers and crew safety is of the utmost importance, they could not have done more to put our health at risk."

Mrs Carrier and her husband, Silvio Rigucci, 64, flew home to Ottawa via Los Angeles and Chicago on March 19, and their friends, Claire Pelletier and Aline Pelletier, travelled on flights the next day.

Mr Rigucci and Mrs Pelletier both tested positive for COVID-19.

All remained in strict home quarantine for 14 days on their return, leaving only for testing.

The notification received by Silvio Rigucci that he tested positive. ( Supplied: Martine Carrier )

Shine Lawyers, who are taking on a class action on behalf of Ruby Princess passengers, said 19 overseas guests had registered with them, including people who had tested positive.

A spokeswoman for the law firm said the potential of the spread worldwide from the ship was "alarming".

"Members of the public in Sydney and abroad were unknowingly exposed to the virus as a result of these passengers' release," she said.

She said people from the US, UK and New Zealand had contacted them after either becoming confirmed cases or experiencing symptoms.

Martine Carrier and husband Silvio Rigucci on the Ruby Princess. ( Supplied: Martine Carrier )

Mrs Carrier said when leaving the cruise on March 19, they were given a piece of paper advising them to go straight to a hotel and stay there until their flight home.

Passengers were allowed to disembark despite several people on board being tested for coronavirus.

The situation has sparked a war of words between the ship's operator, and state and federal authorities.

The ship and its 1,000 remaining crew members is docked at Port Kembla, and is the subject of a police investigation.

"All four of us were lucky that the symptoms were not severe and did not worsen, but our two friends are over 70 years old and my husband is asthmatic so we were worried for a while," Mrs Carrier said.

"We have all recovered now."

Mrs Carrier and her husband made it back to Canada at 10:00pm local time on March 19, but were phoned at midnight by Australian health authorities who told them there had been four cases of COVID-19 on the ship.

"We were absolutely shocked," she said.

The next day Mr Rigucci started to display symptoms and the pair went for testing.

Mrs Carrier said they received an email from Princess Cruises on March 21 advising them that "several guests" on the cruise had been diagnosed with COVID-19.

"These guests were diagnosed after disembarking but were likely infectious while on the ship," the letter said.

A sick crew member is taken off the Ruby Princess earlier this month. ( ABC News )

So far, Princess Cruises has not provided information on how many international passengers have tested positive to the virus.

NSW Police Commissioner Mick Fuller has also said "about 200" of the crew that remain on the Ruby Princess had shown coronavirus symptoms.

So far, 66 of them have tested positive for COVID-19.

Mrs Carrier said international passengers had been overlooked.

"Absolutely we were forgotten," she said.

Police officers in protective clothing raided the Ruby Princess last week. ( Supplied: NSW Police )

NSW Health said it was continuing to provide daily updates on COVID-19 cases and to identify the source of infection if known.

A Princess Cruises spokesman said all disembarking passengers, regardless of where they came from, were told the current requirements at the time, which were to go directly home and undertake 14 days of self-isolation.

"This requirement … applied to all arrivals from a foreign port, whether arrival into Australia was by air or sea," he said.

"As we have stated many times, Ruby Princess followed the federal and state health clearance processes to the letter."

When asked if the company was aware of any cases that had emerged among international passengers, the spokesman said that was a matter for NSW Health.