NSW Health has been unable to contact four Australians who returned from Cambodia over the weekend and who need to remain in self-isolation due to coronavirus fears.

The department was informed of the arrival of more than 20 Australians who had travelled on a cruise ship that had one confirmed case of COVID-19 only two days after they landed in Sydney.

The MS Westerdam docked in Sihanoukville, Cambodia. Getty Images

The Australians had been passengers on the MS Westerdam, which was turned away by several Asian countries before docking in Sihanoukville, Cambodia, last week.

Authorities tested 2200 passengers and crew and declared them free of COVID-19. However, an 83-year-old US woman, who was entering Malaysia and who had left the ship just two days earlier, was found to be infected.

A NSW Health spokesman said on Monday the department was given the email addresses of 22 Australians who had returned to Sydney from Cambodia on Saturday.

"NSW Health immediately sought to make contact with the passengers, asking them to self-isolate as per the national guidelines," he said.

Dr Anthony Fauci, director of the US National Institutes of Allergy and Infectious Diseases, said at the Council on Foreign Relations that the Diamond Princess cruise ship in Japan could reveal potential "modalities of transmission."

"NSW Health has been able to speak to 18 of the passengers and the remaining four have been emailed asking to make contact.

"NSW Health has requested the Commonwealth seek further contact details for these remaining four people."

The spokesman said Holland America Lines, the company that owns the Westerdam, told the department two non-Australians had also arrived in Sydney from Cambodia, and they were assessed and placed in self-isolation.

"The people NSW Health has been able to reach are all well. NSW Health will follow up and monitor these residents and ensure their health needs are managed should they develop any symptoms," the spokesman said.

The Department of Home Affairs said it was a matter for the federal Department of Health.

A spokeswoman for the federal Department of Health said it was providing "direct support" to Australian passengers and crew of the Westerdam.

"The Westerdam is arranging for Australian passengers to return to Australia by commercial means," she said.

"While it is considered very low risk as the Westerdam did not visit China, all people who were on the Westerdam who have returned to Australia should self-isolate for 14 days of leaving the vessel."

The spokeswoman said the department was helping states and territories contact all passengers who had returned.

"We urge passengers who have returned to Australia after disembarking the Westerdam to contact the public health unit in their state for advice," she said.

One passenger from the Westerdam has returned home to Victoria and a spokesman for Victorian health authorities said the person had been assessed and placed in self-isolation. Queensland Health has also been in contact with passengers who have returned to that state, a spokesperson said, and those people have been advised to remain in self-quarantine for 14 days.

At least 79 Australians were on the ship. Ten are still in quarantine on board, 39 stayed in Phnom Penh, 30 have left Cambodia and, of those, at least 22 have returned to Australia.

Passengers told the Herald and The Age that Australian embassy officials told them not to attempt to travel through South Korea, Taiwan, Thailand, Singapore or Malaysia on their way home, and there are no direct flights between Pnhom Penh and Australia.

In Japan, passengers have begun disembarking from the virus-hit Diamond Princess cruise ship after spending two weeks in quarantine off Yokohama, near Tokyo.

Public broadcaster NHK said about 500 people, including about 200 Australians, began disembarking on Wednesday with the entire process to be completed by Friday.

The last 36 Australians who were in quarantine on Christmas Island have boarded flights home, the island's administrator Natasha Criggs said.

with James Massola, Melissa Cunningham, Stuart Layt, Reuters