A new video appears to show doctors collapsing in a hospital in China as the deadly coronavirus mutates and continues to spread.

Three cases of the deadly coronavirus have been confirmed in New South Wales, bringing the total nationwide to four.

NSW Health tonight confirmed three men – aged in theirs 30s, 40s and 50s – are being treated in Westmead Hospital in Sydney and are in isolation.

Victorian Health Minister Jenny Mikakos said this afternoon that a case of the respiratory condition had been confirmed in a man who last week returned from China. The man, aged in his 50s, was in Australia for six days before being diagnosed.

A total of 42 people have died and more than 1300 have been infected so far in China, where the city of Wuhan is considered the epicentre of the virus.

NSW Health Minister Brad Hazzard said 18 people across the state have now been assessed for the virus after samples were sent to a “world-leading” laboratory in Victoria, with 12 patients being “excluded” and three being confirmed on Saturday.

All three men arrived on flights from China – one on January 6, one on January 19 and the other date is being checked by authorities.

“I’d like to thank each of these three people because they have been exemplary in the way that they presented themselves (to health services),” Mr Hazzard told reporters tonight.

He labelled it a “tricky” and “evolving” virus and said the six other cases are under investigation.

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The Victorian case was the first confirmed case in Australia of “about a dozen” being investigated nationwide, an estimate put forward by Queensland’s Chief Health Officer Dr Jeannette Young on Saturday.

“It’s an evolving number,” she told reporters at a press conference on Saturday afternoon.

“We will be treating them as if they’re confirmed cases, as a precaution.

“We still don’t understand the transmissibility of this virus,” Ms Young explained, noting that treatment is symptomatic.

“If you develop fever, coughs or shortness of breath, you should ring ahead to your GP, discuss it and your GP will refer you to the emergency department.”

Queensland Health shared some good news in an update on Saturday night.

“Five people being assessed in Queensland for the Wuhan coronavirus have tested negative to the disease,” the department said.

Dr Young said one more person was being tested but their results will be available on Sunday.

She said they were taking “all precautions possible” and had stepped up their response with the State Health Emergency Coordination Centre. Public hospital emergency departments across Queensland will be instructed to waive testing fees for foreign nationals suspected of carrying coronavirus.

The man with a confirmed diagnosis in Victoria is a Chinese national. He is in a stable condition at the Monash Medical Centre in Clayton, in Melbourne’s southeast.

The man flew in from Guangzhou in China to Melbourne about 9am on January 19 on China Southern Airlines flight CZ321.

Ms Mikakos said there was no cause for alarm for the community, as the patient was isolated and there were no other suspected cases.

Victoria’s acting chief health officer, Dr Angie Bone, said the man was being cared for in a negative pressure isolation room for a “type of pneumonia”, which is expected with this kind of coronavirus.

“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.”

The man had been staying with family and had not been out and about so the risk to the broader community was minimised, she added.

Australia’s chief medical officer Professor Brendan Murphy said it was important for people arriving from Wuhan, and those in close contact with them, to monitor for symptoms including fever, cough, sore throat, vomiting and difficulty breathing.

“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, the Department of Foreign Affairs has overnight 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 border measures to be enhanced.

For those planning on travelling to the region, authorities suggested checking the Smart Traveller website for the latest on the situation.

Australia is the 11th country to have a confirmed case across the globe, authorities said.

NSW chief health officer Dr Kerry Chant said she understood Victorian authorities were contacting people in the rows “before and after” where the confirmed case was sitting on the plane.

She said NSW health authorities are also taking “precautionary” action.

“We’re contacting many people and we do not want them to be unduly alarmed but we do want them to be conscious of the symptoms and we will be following them up to make sure they are well,” she said.

“We do not understand yet the transmissibility of this virus.”

She said testing took about six hours but that time frame would likely shrink in the future.

“It is important that we detect cases early,” Dr Chant said.

“We’re encouraging people who have come back from Wuhan, or who have been in contact with confirmed cases in China or in other countries, to please seek care if you develop any symptoms of fever, sore throat, pneumonia, a cough or respiratory symptoms of any sort.”

Three international teams – including a team of researchers from University of Queensland – are working around the clock to develop a vaccine for the virus.

UQ scientists with the weight of the world on their shoulders: one of three places chosen to develop a vaccine for #coronavirus. They hoped for 3 years - they have 16 weeks. ‘ we always knew this call would come’ @7NewsBrisbane @UQ_News pic.twitter.com/I7kIAJwSxK — Erin Edwards (@ErinEdwards7) January 24, 2020

Health authorities are reminding people of the simple things they can do to reduce their risk of contracting the disease.