NSW Health Minister Brad Hazzard said the male healthcare professional, who was in ICU, had been working in a "clinical situation" and had direct contact with patients.

NSW Chief Health Officer Dr Kerry Chant did not disclose in which hospital the healthcare professional worked, but would provide further information once NSW Health has contacted all of his close contacts.

NSW Chief Health Officer Dr Kerry Chant conceded the confirmed case in the doctor means it is possible cases of COVID-19 have been missed.

“It’s always possible there’s a case out there we could have missed,” she said.

"Our first job is to contact staff or patients that have been in close contact with this person."

Despite the potential that cases have been missed, Dr Chant said health authorities in Australia remained vigilant.

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“We are doing lots of testing. We have tested over 3500 people, and we continue to see high rates of testing,” she said.

She added anyone who has been to Iran should remain “particularly vigilant” of COVID-19 symptoms.

Mr Hazzard said the health department was being transparent about what they knew so far of the new cases, and the community should be “cautious and not alarmed”.

“I won’t be changing anything about what I do on a daily basis,” he said.

Search for contacts continues

NSW Health is also searching for the unsuspecting passengers who were seated near a woman diagnosed with the new coronavirus on a Qatar Airways flight from Doha to Sydney.

The woman in her 50s became the sixth confirmed case of COVID-19 in NSW after returning to Australia from Iran.

She arrived in Sydney on flight QR908 from Iran at 6.50pm on February 23 and started to feel ill almost immediately.

"Anyone on that flight … should be very aware that there was someone on the flight who had the coronavirus," Mr Hazzard said at an earlier press conference on Monday.

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The woman did not keep her flight ticket and her seat number is not known, NSW Chief Health Officer Kerry Chant said.

NSW Health is in contact with the airline to determine where she sat and to identify passengers who sat in the two rows in front of, and behind, her to alert them to the possibility that they may have been exposed to the coronavirus, Dr Chant said.

Those "close contacts" will be asked to self-isolate for 14 days, she said. "We will be reaching out as soon as we have [their] contact details."

Mr Hazzard said any passengers on the flight with flu-like symptoms should contact their doctor.

"If you have any doubts or thoughts that [it] may be the coronavirus, please ring ahead to your GP or ring ahead to the local emergency department so they are aware and can take the appropriate steps to keep everyone safe," he said.

On Monday morning, 80 people in NSW were waiting for coronavirus test results. The number of people assessed for the virus fluctuated daily, Mr Hazzard said.