There are urgent calls to track down and quarantine all former passengers of a cruise liner which docked in Cambodia last week after being turned away by six other Asian countries.

It turns out those other nations were right to be sceptical of claims nobody had been taken ill on the MS Westerdam after an American tested positive for the coronavirus after leaving the ship.

Cambodia said earlier that all 1455 passengers — including 79 Australians — on the Holland America-operated ship had tested negative for the virus.

Now there are fears hundreds of passengers have unwittingly carried the virus to their home countries, including Australia.

Coronavirus has infected more than 71,200 worldwide and killed at least 1770.

If the virus is allowed to spread uncontained around the world, tens of thousands more people could be infected.

“This could be a turning point,” US infectious disease expert William Shaffner said of the shock development.

“We have potentially many (infected former passengers) in many countries, and all it would require is just the establishment of another outbreak in another country and that could potentially tip the scales.”

The 83-year-old American woman was among 145 passengers who flew from Phnom Penh to Kuala Lumpur on Friday after Cambodia put an end to two hellish weeks at sea by agreeing to let the vessel dock at Sihanoukville.

Cambodian Prime Minister Hun Sen greeted scores of disembarking passengers without wearing a mask or gloves, sparking fears he exposed himself to the deadly coronavirus.

The elderly American tested positive to the coronavirus after arriving in Malaysia and health authorities confirmed her diagnosis with a second test. Her husband also had symptoms but has so far tested negative.

All but the American couple were eventually allowed to continue to their destinations, including airports in the United States, the Netherlands and Australia.

Australians David and Judy Holst, who touched down in Adelaide at the weekend, were among the scores of Westerdam passengers who disembarked on February 14 and travelled to Phnom Penh and Kuala Lumpur alongside the infected woman and her husband.

“It’s been ugly but the end is near and it’s a happy ending … see you soon and yes, it is safe to kiss us — we’ve already been in effective quarantine for two weeks,” Mr Holst told Adelaide Advertiser on Friday, before the American fellow passenger tested positive for coronavirus.

There is no suggestion the Australian couple is infected with the virus.

The latest threat comes as Australian authorities prepare to evacuate Aussies stranded on the Diamond Princess — which has more than 355 coronavirus-infected passengers — to Christmas Island for quarantine

However, the Australian government seemed unaware of the risk posed by firmer Westeredam passengers who have been allowed leave the ship and return home. has contacted both the Federal Health Department — which said it was not its responsibility — and the Department of Foreign Affairs and Trade for comment.

Malaysia acted swiftly following the American woman’s surprise diagnosis, turning away two more planes full of Westerdam passengers that were due to land on Saturday.

Deputy Prime Minister Wan Azizah Wan Ismail said the country would also bar all cruise ships from Chinese ports from docking.

Taiwan is also taking the threat seriously, with the Kaohsiung Department of Health asking taxi drivers who had driven passengers to report in for health checks, according to The Taipei Times.

As of Sunday, 233 passengers and 747 crew members were still on the ship docked at Sihanoukville, Cambodia, Holland America said. The more than 1000 other passengers departed Sihanoukville on charter flights to Phnom Penh and were in various stages of transit home, the cruise line said.

“We anticipated glitches, but I have to tell you I didn’t anticipate one of this magnitude,” Dr Shaffner told The New York Times.

He urged countries who had citizens on board to track them down immediately and place them in quarantine for a further two weeks.

Another specialist, Dr Eyal Leshem, director of the Center for Travel Medicine and Tropical Diseases at the Sheba Medical Center in Israel, described the development as “extremely concerning” and said Westerdam passengers who had travelled on from Kuala Lumpur increased the risk of a pandemic.

“We may end up with three or four countries with sustained transmission of the virus,” he told The Times.

“It may be more and more difficult to make sure this outbreak is contained only within China.”

Chinese health authorities have warned the virus can still spread when a patient is asymptomatic and that the incubation period can be up to 24 days.

There have been multiple cases in China of people having tested negative for several days — even when displaying symptoms — before finally returning a positive result.

Holland America’s Westerdam cruise ship took on 800 passengers in Hong Kong on February 1 and was due to travel to the Philippines, Taiwan, Japan and South Korea.

But all those countries rejected it — Taiwan did accept them for one day before changing its mind — along with the US territory of Guam and Thailand.

After docking in Sihanoukville, Holland America informed passengers that the Pasteur Laboratory in Phnom Penh had agreed to accept and test “20 samples taken aboard” for the virus.

“We sincerely thank all those in Cambodia who have demonstrated a willingness to welcome us with an open mind and make decisions based on facts,” it said.

Holland America Line told in a statement it was working closely with government and health officials in Malaysia and Cambodia, and experts from the US Centers for Disease Control (CDC) and the World Health Organization (WHO).

“At this time, no other guests or crew, either on board or on their way home, have reported any symptoms of the illness,” it said.

“Guests who have already returned home will be contacted by their local health department and be provided further information.”

Holland America Line Chief Medical Officer Dr Grant Tarling said the company was “in close coordination with some of the leading health experts from around the world”.

“These experts are working with the appropriate national health authorities to investigate and follow-up with individuals who may have come in contact with the guest,” he said.

No other guests or crew, either on board or on their way home, have so far reported any symptoms of the illness, the company said.

An updated statement on the company’s website said the ship’s next scheduled cruise on February 29 had been cancelled.

On Friday Mr Holst told The Advertiser the Westerdam captain “woke us all up at midnight” to announce all the tests were negative.

“At 1.30am we got woken up again to say ‘you’ve got a flight (home), put your bags out’,” he said.

He said the couple would travel by bus to a local airport, then by charter plane to Kuala Lumpur where they would board a commercial flight to Singapore, then Adelaide.