New South Wales Health says they have confirmed three case of the deadly coronavirus, bringing the national number to four.

Key points: A Chinese man in his 50s is being isolated in a Melbourne hospital with a confirmed case of novel coronavirus

A Chinese man in his 50s is being isolated in a Melbourne hospital with a confirmed case of novel coronavirus Another three cases have been confirmed in NSW

Another three cases have been confirmed in NSW The virus has so far killed at least 41 people in China and sickened more than a thousand more

All three NSW cases are being treated in hospitals across Sydney.

They are men aged in their 30s, 40s and 50s and contracted the illness in China.

One of the men arrived in Australia on January 6 and another arrived on January 19.

The third man arrived on January 20 but only presented to hospital the following day.

Chief Medical Officer Dr Kerry Chant says she does not believe they were contagious on the flight to Australia as their symptoms did not become apparent until they were in Sydney.

Dr Chant says details of the January 20 flight will be released in the coming days.

NSW Health Minister Brad Hazzard says four other cases are currently under investigation.

Some of those being tested are children.

The first Australian case of coronavirus was confirmed earlier today with a man being held under isolation in a Melbourne hospital as health authorities warn more people are likely to be carrying the disease.

News of the case came as Chinese authorities said the death toll from the outbreak of the new strain of the virus had jumped to 41, with 1,287 confirmed cases.

NSW Health have tested and cleared 12 people.

The Melbourne patient is a Chinese man in his 50s who recently spent time in the city of Wuhan, where the deadly outbreak is believed to have originated in an illegal wildlife market.

He is in a stable condition at the Monash Medical Centre.

His case has sparked concerns among health officials that more people with the virus may have arrived in Australia before Wuhan was locked down.

"Given the number of cases that have been found outside of China and the significant traffic from Wuhan city in the past to Australia it was not unexpected that we would get some cases," Australia's Chief Medical Officer Professor Brendan Murphy said.

"The risk to Australia I think is more in those people who travelled in the week up to last Thursday when the travel ban was put in place.

"There are potentially others like this person who have travelled to Australia who were well when they arrived who may develop the disease."

But he moved to reassure the public that the risk from the disease was low.

"Unless you have come into contact with someone who is unwell from that part of China, there is no need for concern," Professor Murphy said.

Melbourne patient's GP failed to raise red flag

The Melbourne coronavirus patient spent two weeks in Wuhan before coming to Australia, arriving in Melbourne on China Southern Airlines flight CZ321 from Guangzhou on the morning of Sunday, January 19, and has been with his family since then.

The first leg of his trip was from Wuhan to Guangzhou.

All the other passengers who were on the man's flight are being contacted and his family is being closely monitored for any signs of illness.

This morning Victorian health authorities said it was "highly likely" more coronavirus infections would be confirmed, but said the risk of the disease spreading from person to person in the general community was low.

Victorian Health Minister Jenny Mikakos said "the gentleman and the family did everything right."

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"He exhibited no symptoms on the flight and when he did experience some symptoms of illness they contacted the GP on Thursday, they called ahead and he was double-masked when he presented to the GP clinic.

"He was not confirmed to have coronavirus by the GP. The family contacted the Monash Medical Centre on Friday, they called ahead of time and again he was masked before he turned up at [emergency] and [was] immediately put into isolation."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 47 seconds 47 s Victorian authorities confirm Australia's first coronavirus case

Victoria's deputy chief health officer Angie Bone said she was concerned that the GP did not link a person coming from Wuhan and a respiratory virus with a possible case of coronavirus, but she was "very glad that the family then brought extra help the following day when he clearly wasn't getting any better."

Dr Bone said the state would increase messaging to GPs and the doctor would be contacted and asked to monitor his own health.

Four people in South Australia are also being tested for the virus, but health authorities say the chances they have the virus are low.

Federal and state health ministers took part in a teleconference this afternoon to discuss Australia's response to the case.

Entire cities in lockdown in China

Europe's first three cases were confirmed in France on Friday, with two patients being hospitalised in Paris and the other in the south-western city of Bordeaux.

On the eve of the Lunar New Year, transportation has been shut down in at least 13 Chinese cities with a combined population of some 36 million people.

At least eight hospitals in Wuhan issued public calls for donations of masks, goggles, gowns and other protective medical gear, according to notices online.

China's Government announced it was sending in military medics to Wuhan.

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

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

China is swiftly building a 1,000-bed hospital dedicated to patients infected with the virus. ( AP: Chinatopix )

Thailand has confirmed four cases, Malaysia has three, Japan, South Korea and the United States have confirmed two cases each, while Taiwan and Singapore have reported one each.

Indian authorities say an Indian nurse working in Saudi Arabia has also been infected, but Saudi health authorities say there has been no cases in the country so far.

Airports worldwide are screening passengers arriving from China, with the US warning travellers to exercise increased caution in China.

Hong Kong, which has two confirmed cases, is turning two holiday camps into quarantine stations as a precaution. Taiwan has banned anyone from Wuhan from going to the island.

Australians urged not to travel to Wuhan and Hubei

The Federal Government has raised travel advice for the province of Hubei, which includes the city of Wuhan, in China to the highest level, due to the threat posed by the coronavirus.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 37 seconds 37 s Australia's chief medical officer provides update on coronavirus

The level four warning urges Australians not to travel to the region.

Foreign Minister Marise Payne said Chinese authorities had restricted travel in at least five Hubei cities and Australians going there may not be able to leave until restrictions are lifted.

Travellers are being warned that the level of assistance the Government can provide is limited.

Prime Minister Scott Morrison said Australians should be assured that all necessary procedures were "swinging into place".

"The confirmation today by Victorian authorities of the coronavirus case was a matter that had been anticipated," Mr Morrison said.

"The Australian Government, of course, has been taking this issue incredibly seriously and we have activated all the necessary precautions and procedures.

"I want to assure Australians our officials, our medical experts, clinicians, our border security officials and agencies, our biosecurity professionals, are working closely together at a Commonwealth and state level.

"I'd urge Australians to go about their day, to go about their business, with the knowledge that professionals and experts — that are there to provide the support that is needed in times like this — are on the job."

On Thursday the Prime Minister said Australia was well equipped in the event of an outbreak of coronavirus, and masks could be made available.

"There are over 10 million protective masks in the national stockpile," Mr Morrison said.

Earlier in the week the Chinese Government stopped all transport out of Wuhan. The last Wuhan flight to arrive in Australia landed in Sydney on Thursday morning, with patients met by health authorities on arrival.

That precaution will continue to be put in place at all Australian airports for flights that arrive from China.