Australian health authorities are warning that the fifth person to test positive to the deadly coronavirus won't be the last and that more cases will emerge.

A 21-year-old Sydney university student has become the country's fifth person to be diagnosed after flying back from the virus's epicentre in Wuhan, China.

Three men - aged 35, 43 and 53 - are also being treated at Sydney's Westmead Hospital and are in a stable condition.

Federal Health Minister Greg Hunt says there's potential for more cases.

Authorities are working to trace all contact the five patients have had, including people who were on the same flights, the minister told Sky News on Tuesday.

NSW Health confirmed five people were also undergoing testing.

A man in his 50s in Victoria is being treated at Monash Medical Centre while four of his family members are under home isolation.

Australian chief medical officer Professor Brendan Murphy said authorities were doing their best to contact people who had been in close proximity to those who had been diagnosed with the virus, but more positive results were inevitable.

"There's people tested every day and there will be more that turn out to be positive," Prof Murphy said.

In the latest case to be identified by authorities, the UNSW student displayed no symptoms upon landing in Sydney on China Eastern flight MU749 last Thursday but 24 hours later began exhibiting flu-like symptoms.

The diagnosis came as some schools around the country took action to segregate students who had visited China.

Ten Chinese pupils at Brisbane's Stuartholme are being isolated to their own floor of the boarding house for two weeks and assessed regularly for illness under the advice of Queensland Health, The Australian reported.

Pymble Ladies College in Sydney and Firbank Grammar School in Melbourne advised parents to keep their children at home for at least two weeks if they had visited an affected area in China.

Other private schools requested students who had visited the affected regions in China provide a doctor's certificate.

China's National Health Commission Minister Ma Xiaowei said the country's health officials believed patients were infectious during the virus' incubation period, which ranges from one-to-14 days.

Until now, doctors have believed patients are only contagious when they start showing symptoms.

But Prof Murphy expressed scepticism and said the government was seeking urgent advice from the World Health Organisation.

"The expert panels were not convinced of that at the moment. They were not convinced that evidence is being presented," Prof Murphy said.

"It would be very unusual because this virus is similar to the SARS and MERS viruses and they were not infectious before symptoms.

"If that were to be the case, it would have implications for contact tracing."