Health officials say there is one more "probable" case of coronavirus in Sydney, and they are on alert for infected travellers who could have slipped through China's quarantine.

Key points: Authorities are trying to track down anyone who was on board China Eastern Flight MU749 on January 20

Authorities are trying to track down anyone who was on board China Eastern Flight MU749 on January 20 The death toll from the virus in China has risen to 56

The death toll from the virus in China has risen to 56 Australia has four confirmed cases, and another probable

NSW Health yesterday confirmed three cases of the deadly disease in the state, bringing the national total of confirmed cases to four, after a man in his 50s in Victoria became the first confirmed case in Australia on Saturday morning.

On Sunday afternoon NSW Health said another four people who had been tested for the virus had been cleared.

Earlier in the day, Australia's chief medical officer Brendan Murphy said he would not be surprised if more cases were to crop up.

"Knowing what's happened in other countries and knowing the traffic from that part of China to Australia, it's highly likely we may see some more," Professor Murphy said.

He downplayed the risk of an outbreak in Australia because Chinese authorities had locked down Wuhan, which is believed to be ground zero for the infection.

"However … people left the province before the lockdown and could come to Australia over a number of flights," he said.

Professor Murphy said every passenger from flights touching down in Australia from China would be given an information sheet asking them to identify if they have symptoms of the disease.

"There is no cause for general concern … there is no risk to Australian population other than people with that travel history or who have been in contact with those people."

"The chances are they won't have this condition, the really important thing in Australia is we identify and be able to isolate people with this virus."

Authorities chasing 'highest risk' travellers

Professor Murphy said both NSW and Victorian health authorities were "working flat-out" to track down passengers who sat within two rows of the infected individuals.

He said these were the passengers with "real potential of any cross-infection" and were at "highest risk".

However, it is proving to be a tedious task, with authorities having to decipher contact details on the landing cards which passengers are required to fill out by hand upon arrival.

Two of the men diagnosed in Sydney on Saturday had travelled to Wuhan, and one person is believed to have had direct contact with a confirmed case while in China.

NSW Health said one of those men arrived in Sydney on China Eastern Flight MU749, which touched down at 11:35am on Monday, January 20.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 2 seconds 1 m 2 s The flight from Wuhan touches down in Sydney on January 23.

Another, in his 30s, arrived in Sydney from China on January 6 but did not develop symptoms until January 15, when he saw his doctor. The third man, aged in his 40s, arrived on January 18 after spending time in Wuhan but did not show symptoms until January 24. Because those travellers did not have symptoms during the flight it is believed the risk of spreading the virus was still relatively low.

"We do not believe that they were infectious at the time of their international flight," NSW chief medical officer Kerry Chant said.

Authorities are urging anyone who has developed symptoms of the virus and was on last Monday's flight to contact their emergency department by phone.

NSW Health says it had been flooded with calls from concerned passengers since Sunday morning.

Authorities have conducted extensive interviews with people who had come into contact with the infected men but conceded the patients may have come in contact with hundreds of people since arriving in the country.

Dr Chant said some cases could have been caught sooner by GPs, and urged doctors treating those with coronavirus-like symptoms to contact NSW Health.

"Make sure you have processes in place and consider where people have travelled and particularly be conscious of people returning from China," she said.

Professor Murphy said updated information would be distributed to GPs and emergency departments across the country after reports a doctor failed to flag a possible infection in Victoria.

"That was one of the reasons prompting me to send [the message out again]," he said.

"We have previously provided information but we are trying to reinforce it."

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

Chinese state media says 13 more people have died from the coronavirus outbreak in the central Hubei province.

Shanghai also reported its first death from the virus, bringing the total number of deaths in the country to 56.

The global infection rate has shot past 2,000 — at least 40 of those cases are outside China.

Eighteen people across NSW have now been tested for the virus, with 12 of those cleared, but two are still under investigation.

Some of those being tested are believed to be children.