A man visiting from Wuhan has been confirmed as the first coronavirus patient in Australia.

Four cases of the deadly coronavirus have been confirmed in Australia, as authorities scramble to contact passengers who shared flights from China with the patients.

Three men tested positive to the respiratory condition in NSW on Saturday, state health authorities confirmed.

It comes after another man, aged in his 50s, tested positive in a Melbourne hospital after arriving from the Chinese city of Guangzhou last week.

A total of 18 people have been tested for the virus in NSW, with 12 of those given the all-clear.

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Nine people in Queensland have returned negative results for coronavirus, with authorities on Saturday still waiting on results from another possible case.

Four people in South Australia were also being tested but authorities said it was unlikely they actually had the virus, with a man also being checked in a Hobart hospital.

While authorities do not fully understand how the coronavirus spreads, it is thought to be less contagious than measles and only transmissible once a patient has started showing symptoms.

Australian Health Minister Jenny Mikakos said on Saturday morning (local time) said the first case of the respiratory condition had been confirmed in a man who last week returned from China.

The Chinese national in his 50s had been in Wuhan, a city of 11 million people which has been the epicentre of the outbreak.

Authorities warn it is "highly likely" there will be other cases in Australia and it is still possible more passengers on this man's flight will be diagnosed with coronavirus.

He arrived in Melbourne on January 19 from China and displayed no symptoms on flight to Melbourne, she said.

The man was confirmed as having coronavirus at 2.15am today (local time).

She said there was no cause for alarm for community, the patient is isolated and there were no other suspected cases.

Mikakos said the risk of transmission remained low but Victorian and commonwealth officials would be stationed at Melbourne Airport and a hotline would be set up for people to get information about coronavirus.

The coronaviruses are a family of viruses that originate in animals before making the jump to humans. The outbreak in China is thought to have originated in a seafood market in Wuhan.

"This is an evolving situation. We are now one of eleven countries who have confirmed cases," Mikakos said.

"I do want to stress... there is no reason for alarm in the general community. We have had flu epidemics in the past, including SARs and our system is geared up well to deal with this situation."

The man has pneumonia and is in a stable condition, she said. Hospital staff treating him are wearing masks, gloves, and gowns while treating the man in an isolated room in the Monash Medical Centre.

The man arrived in Melbourne at 9am (local time) on on January 19 on a China Southern Airlines flight CZ321 from Guangzhou.

The minister stressed the man had spent his time since arrival with relatives at their home.

Authorities are scrambling to track down passengers who flew to Melbourne from mainland China six days ago along with a man infected with the deadly coronavirus in the first confirmed case in Australia.

GETTY IMAGES Passengers arrive at Sydney International Airport on January 23, 2020.

Australian Federal Health Minister Greg Hunt said Victorian and Commonwealth authorities would undertake "contact tracing" for passengers who had travelled on the January 19 flight and would provide them with "information and advice".

Victorians and visitors returning from Wuhan City or other locations cases have been detected are being urged to closely monitor their health.

Five people are undergoing testing for the virus in NSW and two in Queensland. A number of people have already been cleared in both states.

TRAVEL BAN EXTENDED TO LOCK DOWN 35 MILLION PEOPLE

China locked down more than 35 million people in an increasingly urgent effort to halt the spread of the deadly coronavirus Friday, as the United States confirmed a second infected person and the respiratory illness found its way to Europe, where the first three cases were announced in France.

AP A policeman uses a digital thermometer to take a driver's temperature at a checkpoint at a highway toll gate in Wuhan.

The pneumonia-like disease has claimed 41 lives - all in China - and infected more than 1,200 people there. An official at the World Health Organisation told reporters that his agency has begun planning for an outbreak that will last for months.

Infections have been confirmed in France, South Korea, Japan, Nepal, Thailand, Singapore, Vietnam, Taiwan, Australia, Malaysia and the United States as the disease spreads outside Asia.

A doctor who had been working on the front line of efforts to control the disease in Wuhan died on Saturday, Chinese state media reported.

Liang Wu dong was 62 and had retired a year ago, according to staff at Hubei Xinhua hospital, but was apparently called back to work to help combat the disease. He fell ill with suspected coronavirus on January 16 before being transferred to another hospital in the city as a patient.

AP Chinese paramilitary police stand guard outside the closed Hankou Railway Station in Wuhan, cutting off access to entire cities with millions of residents.

A ban on travel was extended to 14 cities in China, with a total population of more than 35 million in central China's Hubei province. Tunnels under the Yangtze River were blocked to stop the flow of traffic, and all ride-hailing services in Wuhan were halted at midday Friday. Only half the city's taxis are allowed on the road each day.

China Southern, the country's biggest airline, had already cancelled flights in and out of Wuhan airport on Thursday. The other two main carriers, Air China and China Eastern, said they would cancel all Wuhan flights from Friday until at least Febuary 8.

As the Lunar New Year began, authorities have cancelled the temple fairs and festivals that normally accompany the nation's biggest holiday. Large public gatherings could aid the spread of the airborne virus.

Nevertheless, state broadcaster CCTV led its midday news program with a report about a huge banquet in Beijing attended by President Xi Jinping and other Communist Party leaders. None of them were wearing a mask, and the report made no mention of the virus outbreak.

GETTY IMAGES A resident wears masks to buy vegetables in the market in Wuhan.

Other senior Chinese officials came under heavy criticism for their slow response to the outbreak. The mayor of Wuhan, Zhou Xian wang, allowed a huge potluck banquet to proceed Sunday, during a weekend when the number of confirmed infections shot up dramatically. The city had arranged a Lunar New Year meal featuring 14,000 dishes for more than 40,000 people, an event it hoped to get listed in Guinness World Records.

Residents were also surprised by photos and video of the two top officials in Hubei province - the Communist Party secretary and the governor - at a dance performance in Wuhan to celebrate the arrival of the Spring Festival holiday. They were sharply criticised for enjoying themselves instead of working on the response to the health crisis.

The Forbidden City in Beijing, which can admit 80,000 people a day and was entirely sold out for the holiday, has been closed until further notice. Shanghai Disneyland, which normally has 10 million visitors a year, announced Friday that it would shut down indefinitely starting Saturday.

SUPPLIED Asia taking no chances with new China virus.

Production companies have postponed the release of seven films over the holiday, prompting Chinese cinema companies to close the country's 70,000 movie theatres.

Schools in Hubei province, due to begin the spring semester after the holiday, will not open their doors as planned but will wait for further guidance from health authorities. The Education Ministry instructed universities around China to delay their opening dates if necessary.

Workers are racing to build a 1,000-bed hospital for people with the disease in Wuhan, an indication that Chinese officials expect, or already have, a much larger number of cases.

AP Trucks line up along a highway near a construction site as China rushes to build a field hospital in Wuhan.

It is modelled after a medical facility specially built in 2003 for patients with SARS, another respiratory infection that began in China and claimed more than 750 lives in more than a dozen countries. The new virus is closely related to the SARS coronavirus.

China's state-run Xinhua News Agency said the new hospital is needed "to address the insufficiency of existing medical resources."

One of the most recent fatalities was a young, previously healthy man in Wuhan, raising concerns about the deadliness of the virus.

He had no chronic diseases or other existing health conditions, and had been treated with anti-viral medication and antibiotics since he was admitted to a hospital on January 9.

AP Workers are racing to build a 1,000-bed hospital for people with the disease in Wuhan.

Until now, the vast majority of victims have been older than 60 with underlying health conditions.

Aside from 1,287 confirmed cases of infection, a total of 8,420 people are reported to be under observation in China.

Despite the escalating toll, some analysts remained concerned that the Chinese government was significantly under reporting the number of cases.

A financial analyst for the US investment firm Raymond James told clients in a report Thursday night that he believes the numbers are likely at least 10 times the publicly reported total.

- SMH and Agencies