Chinese scientists say they have successfully isolated the strain of coronavirus that has caused dozens of deaths in central China - a crucial step in creating a vaccine.

Xu Wenbo, the director of the Institute for Viral Disease Control at China's Centre for Disease Control and Prevention, made the announcement to reporters on Sunday.

Meanwhile, China's southern Guangdong province has ordered all residents to wear face masks when outdoors as efforts continue across the country to prevent the spread of the virus.

Health authorities are investigating three fresh possible cases of coronavirus in NSW while three men who have been diagnosed with the deadly viral infection remain isolated in hospital.

1/2 @NSWHealth is urging people who have recently returned from #Wuhan or have been in contact with a confirmed case of #novelcoronavirus infection to ensure they are aware of the symptoms and seek immediate health assessment if symptoms develop within 14 days. pic.twitter.com/BzPKqJlcKV — NSW Health (@NSWHealth) January 25, 2020

NSW Health on Sunday confirmed there were a total of five cases under investigation.

Earlier, two people had been cleared, temporarily bringing the number of cases being investigated to two, however that was revised.

"Yesterday we reported we had four cases that were under investigation," NSW Health Minister Brad Hazzard said.

"We're very pleased to say two of those four cases have been cleared.

"It is, however, a moving feast in terms of the number of people coming forward.

"We have at the current time another three people under investigation. That gives us a total of five who are having their pathology addressed."

EPA

The three infected men, aged 35, 43 and 53, have been isolated in hospital to prevent the virus spreading further and are listed as being in a stable condition.

Two of the men had travelled to the Chinese city at the centre of the outbreak - Wuhan - while another man had travelled from the southern city of Shenzhen but had direct contact with a person from Wuhan who was diagnosed with the virus.

2/2 The most common symptom is a fever. Other symptoms include , cough, sore throat and shortness of breath.



Read the full media release

English: https://t.co/Le4Q3sRpPP

Mandarin: https://t.co/RhsYFfhZaZ



Find out more about novel coronavirus: https://t.co/461CdHG1Ct — NSW Health (@NSWHealth) January 25, 2020

Chief health officer Kerry Chant said anyone who has symptoms of the deadly infection should cover their coughs and sneezes with a tissue or their elbow and wash their hands thoroughly.

Am I at risk? NSW Health’s Chief Health Officer Dr Kerry Chant advises the community to take Novel coronavirus seriously. Find out more: https://t.co/461CdHG1Ct #novelcoronavirus #2019nCoV pic.twitter.com/KyyPABTYhg — NSW Health (@NSWHealth) January 26, 2020

Symptoms include fever, cough and difficulty breathing.

Dr Chant said people shouldn't be afraid of speaking to their doctors if they experience any coronavirus symptoms.

NSW Health Minister Brad Hazzard also urged anyone with symptoms to come forward.

Mr Hazzard said the state's health department had done everything possible to identify and contain the virus.

READ MORE Australia confirms four coronavirus cases as authorities rush to stop spread

China has confirmed 56 deaths from the virus, while some 1300 people are now estimated to have the virus worldwide.

The illness has been confirmed other countries including Thailand, Japan, South Korea, Hong Kong, Singapore, France and the United States.

Australians are being urged not to travel to Wuhan or China's Hubei province.