Health authorities say a young female Chinese student is the likely to be the fifth case of the deadly coronavirus in Australia.

Professor Brendan Murphy, the federal government's chief medical officer, told Today she is in isolation and had preliminary tested positive to the virus.

"She is in isolation until the final confirmation. But NSW Health feel she's likely to be the fifth case in the country," Prof. Murphy said.

Authorities are currently trying to track down people she has been in contact with.

Prof. Murphy said more confirmed cases are likely to emerge over the coming days.

"Public health follow-up of this probable case is being undertaken in accordance with the national guidelines and the patient remains in isolation," NSW Health said in a statement.

NSW Chief Health Officer Dr Kerry Chant speaks to the media at a press conference on coronavirus. (AAP/Bianca De Marchi) (AAP)

The coronavirus as seen under a microscope. (British Health Protection Agency)

They said they expected to confirm their diagnosis today clearing four patients who had undergone testing.

Three patients in NSW and one in Victoria have already been diagnosed with the virus after an outbreak centred in the Chinese city of Wuhan which has spread across the world.

Three men aged 35, 43, and 53 are being treated in a Sydney hospital but are listed as being stable and NSW Health Minister Brad Hazzard on Sunday said he was pleased with their progress. Authorities have now spoken to all but two people who have been in close contact with the three men since they arrived from China.

"There are a small number of people we're still trying to contact but substantially we have made contact," NSW chief health officer Dr Kerry Chant said.

'No case for mass panic', warns expert

Professor Dominic Dwyer from NSW Health told Today it was important to remain vigilant rather than "alarmed" over growing cases.

"I think we are certainly in a situation of being alert, if not alarmed. I think the important thing is we are seeing cases developing in China quickly," he said.

"We are monitoring, of course, a return of people from China to Australia very rigorously and we have identified a couple of cases, but we certainly haven't seen large numbers of cases or any spread of the virus in Australia."

Prof. Dwyer also said authorities should ensure up to 100 young Australians in the provinces around Wuhan awaiting return are healthy before they land in Australia.

"The main thing is making sure that they're well when they come back. If they haven't got any problems, there's no problem with them coming back at all provided they are well," he said.

Police Officers wear masks at Narita Airport in Narita, Japan, as cases of the coronavirus spread. (AAP)

"If they are not well though, they would be monitored in the way we are monitoring everybody returning back from China."

Prof. Dwyer said it was not yet necessary to bar people travelling from infected parts of China.

"I don't think there is a problem with people coming from affected areas, provided they are screened and we determine whether they've had any exposure to people who have been sick or they've been in parts of China where it has been in parts of China where it has been in transmission," he said.

He also cautioned against people with runny noses and other symptoms assuming they had the coronavirus.

"I think if people haven't been in China or haven't had contact with anyone who has got the disease, the likelihood-them having this virus is in fact extremely low," he said.

"They are much more likely to have a common cold or some other less important infection."

(9News)

The priority remains ensuring overseas visitors are vigilant in reporting any symptoms to avoid the spread of the virus.

Advice to GPs

Prof Murphy says he will be sending out a message to GPs across the country on how to handle patients who present with symptoms of the deadly illness.

"There is no cause for general concern," Prof Murphy told reporters in Melbourne on Sunday.

"I would not be surprised if there are some more cases ... it's highly likely that we may see some more.

"We are incredibly well prepared to isolate and deal with that."

The three men who were yesterday confirmed to have the virus are aged 53, 43 and 35 and all had some connection with the Hubei province.

The patients are being kept in the same isolation facilities as people who contract measles, which is considered a more contagious illness.

NSW chief health officer, Kerry Chant, has confirmed public health units have contacted the majority of the patients' close contacts to warn them of the risk.

"The risk of those transmission to those people is very, very low but these are precautionary actions," she said.

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

The Victorian patient, a Chinese national, has been isolated at the Monash Medical Centre in Clayton after his results returned a positive test at 2.15am on Saturday.

"He was confirmed as positive after a series of tests early this morning," Victorian Health Minister Jenny Mikakos told reporters.

A Chinese health worker waits to check the temperature of travellers entering a train station during the Chinese New Year and Spring Festival on January 25, 2020 in Beijing, China. (Getty)

"What I can advise you is that the gentleman has been in the city of Wuhan in China for the past two weeks prior to the onset of his illness."

Ms Mikakos said the man arrived on a China Southern Airlines flight, flight number CZ321, from Guangzhou to Melbourne last Sunday.

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.

The US is arranging a charter flight today to bring its citizens and diplomats back from Wuhan, the central Chinese city at the epicentre of the outbreak, the Wall Street Journal reported.

Chinese Lunar New Year overshadowed by virus

President Xi Jinping says China is facing a "grave situation" as the death toll from the coronavirus outbreak jumped to 42, overshadowing Lunar New Year celebrations.

Hong Kong has declared a virus emergency, scrapped celebrations and restricted links to mainland China, while Australia confirmed its first four cases on Saturday.

A Chinese health worker checks the temperature of a woman entering a subway station during the Chinese New Year and Spring Festival on January 25, 2020 in Beijing, China. (Getty)

In Hong Kong, leader Carrie Lam said her government will raise its response level to emergency, the highest one, and close primary and secondary schools for two more weeks on top of next week's Lunar New Year holiday. They will reopen February 17.

Lam said direct flights and trains from Wuhan would be blocked.

In a sign of the growing strain on Wuhan's health care system, the official Xinhua news agency reported that the city planned to build a second makeshift hospital with about 1,000 beds. The city has said another hospital was expected to be completed on February 3.

Chinese women and a child all wear protective masks after celebrations for the Chinese New Year and Spring Festival were cancelled by authorities on January 25, 2020 in Beijing, China. (Getty)

The new virus comes from a large family of what are known as coronaviruses, some causing nothing worse than a cold. It causes cold and flu-like symptoms, including cough and fever, and in more severe cases, shortness of breath. It can worsen to pneumonia, which can be fatal.

China cut off trains, planes and other links to Wuhan on Wednesday, as well as public transportation within the city, and has steadily expanded a lockdown to 16 surrounding cities with a combined population of more than 50 million - greater than that of New York, London, Paris and Moscow combined

China's biggest holiday, Lunar New Year, unfolded on Saturday in the shadow of the virus. Authorities cancelled a host of events, and closed major tourist destinations and movie theatres.

Temples locked their doors, Beijing's Forbidden City and Shanghai Disneyland closed, and people cancelled restaurant reservations ahead of the holiday, normally a time of family reunions, sightseeing trips and other festivities in the country of 1.4 billion people

Temples and parks were decorated with red streamers, paper lanterns and booths, but some places started dismantling the decor.

People in China wore medical masks to public places like grocery stores, where workers dispensed hand sanitiser to customers. Some parts of the country had checkpoints for temperature readings and made masks mandatory.

Australians advised not to travel to Wuhan or China's Hubei province

The Department of Foreign Affairs and Trade has raised the level of travel advice for Wuhan and Hubei province to "do not travel" while the disease is now listed as having "pandemic potential" allowing boarder measures to be enhanced.

"China has been very helpful in sharing the genome sequence with us so we have a very good test and we can be absolutely categorical about whether this is the situation or not, and that is the situation in this case."

A thermal scanner checks on arriving passengers at Manila's international airport, Philippines. The government is closely monitoring arrival of passengers as a new coronavirus outbreak in Wuhan, China has infected hundreds and caused deaths in that area. (AP)

Experts are still learning about the virus and Australia's Chief Medical Officer Brendan Murphy says it's important people arriving from Wuhan, as well as those in close contact with them, look out for symptoms of fever, cough, sore throat, vomiting and difficulty breathing.

Heavy equipment works at a construction site for a field hospital in Wuhan in central China's Hubei Province.

"We don't know exactly how long symptoms take to show after a person has been infected but there is an incubation period and some patients will have very mild symptoms," Prof Murphy said.

Meanwhile, China has expanded its lockdown against the deadly new virus to an unprecedented 36 million people and rushed to build a prefabricated, 1000-bed hospital for victims as the outbreak cast a pall over Lunar New Year, the country's biggest, most festive holiday.

The World Health Organisation has declared the new coronavirus an "emergency in China" but stopped short of declaring it of international concern.

Millions stranded

Wuhan, a city of 11 million at the centre of the outbreak, is in virtual lockdown. Nearly all flights at Wuhan's airport have been cancelled and checkpoints blocked the main roads leading out of town on Friday.

As the city slides into isolation, pharmacies have begun to run out of supplies and hospitals have been flooded with nervous residents. The city is rushing to build a 1000-bed hospital by Monday, state media said.

The facility will be a prefabricated structure on a 25,000 sq m lot, slated for completion February 3.

Heavy equipment works at a construction site for a field hospital in Wuhan in central China's Hubei Province. (Chinatopix via AP)

Despite the lockdown, the virus is already spreading further afield.

The vast majority of the cases and all of the deaths have been in China, but it has also been detected in Thailand, Vietnam, Singapore, Japan, South Korea, Taiwan, Nepal and the United States.

France today has confirmed its first two cases of the virus, with one patient being hospitalised in Paris and the other in the southwestern city of Bordeaux.

Health Minister Agnes Buzyn told a news conference these were the first two confirmed cases in Europe and that more cases were likely to occur in France.

Virus spreads to Europe

Earlier, the charity SOS Medecins said it had treated a 48-year-old patient of Chinese origin who was showing symptoms of a fever and who said he had been in contact with people from Wuhan.

The patient had returned to France two days ago from a trip to China which included a stop in Wuhan.

"He's been put in an insulated room so as to avoid any contact with the outside world. He's fine," Ms Buzyn said.

The US Centers for Disease Control and Prevention said on Friday it had 63 patients under investigation, with two confirmed cases, both in people who had travelled to Wuhan.

Following a congressional briefing by health officials, Republican Senator John Barrasso, a former physician, said people in the United States with the virus may have been infected as long as 14 days earlier in China.

"We want to try to stop and prevent people from coming to the United States if they have it," Barrasso told reporters, without providing any details of how that might be accomplished.

Airports around the world have stepped up screening of passengers from China.

The newly-identified coronavirus has created alarm because there are still many unknowns surrounding it, such as how dangerous it is and how easily it spreads between people. It can cause pneumonia, which has been deadly in some cases.

Symptoms include fever, difficulty breathing and coughing. Most of the fatalities have been in elderly patients, many with pre-existing conditions, the WHO said.