There are fears an infected Sydney doctor may have spread the coronavirus to a large number of patients, after six more people tested positive in NSW overnight.

Forty staff members who work closely with the 53-year-old male doctor at Ryde Hospital have been isolated.

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They include 13 doctors, 23 nurses and four other health workers. The infected doctor is in a stable condition at Westmead Hospital

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Medical workers in protective suits move a coronavirus patient into an isolation ward at the Second People's Hospital in Fuyang. Photo / AP
Medical workers in protective suits move a coronavirus patient into an isolation ward at the Second People's Hospital in Fuyang. Photo / AP

However, authorities say the doctor had already come into contact with a "large and diverse" range of patients in his workplace.

"We still don't know how he acquired the infection," NSW chief health officer Kerry Chant said.

"We are doing an investigation as we speak. He did not care for any of our positive cases but we are doing some additional investigations into what patients he saw, to see whether there were any undiagnosed cases."

Authorities are now struggling to track potential victims after it's been confirmed one of the new cases is a human-to-human transmission inside Australia.

In that case, the virus spread to a NSW woman in her 50s who had not travelled outside of Australia recently.

A further eight patients of the doctor are showing no symptoms, while 29 other patients identified as casual contacts are being chased up.

NSW Health is alerting passengers who were on five separate flights from Asia in the past week after two men in their 30s, a man in his 50s and two women in their 60s tested positive following their arrival in NSW.

The men in their 30s travelled from Iran, the two women flew from Japan and South Korea respectively, and the man in his 50s was returning from Singapore.

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And health authorities are advising passengers who sat near a coronavirus-infected woman on a Doha-to-Sydney flight to immediately isolate themselves at home.

Medical workers in protective suits move a coronavirus patient into an isolation ward at the Second People's Hospital in Fuyang. Photo / AP
Medical workers in protective suits move a coronavirus patient into an isolation ward at the Second People's Hospital in Fuyang. Photo / AP
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The woman in her 50s who flew into Australia from Iran on February 23 aboard Qatar Airways flight 908 from Doha was in seat 43H.

Another locally acquired case in Sydney is a 41-year-old sister of an infected man who recently returned from Iran where the virus is rampant.

As the hunt for virus victims ramps up state and federal authorities are clashing over the "tracing" measures used to find them, after NSW authorities say they've hit a stumbling block.

They are trying to get hold of passenger cards for people who sat on the high-risk flights near infected people, but say the process has been a struggle.

Chant has called on the federal government to introduce a "streamlined" way to get the details of those on the at-risk flights.

She said authorities were still waiting for the Australian Border Force to provide cards for people who sat near an infected woman who flew into Sydney on February 23 aboard Qatar Airways flight QR908 from Iran.

However, the federal government says there are no delays in providing health authorities with incoming passenger cards.

"We are making sure we get in contact with them and make sure they don't have symptoms," Hazzard said. "It's a bit of a worry."

The latest NSW infections bring total number of coronavirus cases in Australia has risen to 40, with more people undergoing tests, including a passenger who landed at Victoria's
Avalon Airport.

Across the globe, more than 90,000 coronavirus cases and 3100 fatalities have been confirmed, including the death of West Australian James Kwan.