The positive result was recorded after 8pm on Saturday, meaning the state's virus-free run will end at 56 days.

NSW Health said in a statement the source of the Sydney worker's infection remains unclear and testing of their close contacts is underway.

There were no locally-acquired COVID-19 cases in the 24 hours to 8pm on Saturday and three cases in travellers in hotel quarantine.

Health Minister Brad Hazzard will address the media later on Sunday.

Prime Minister Scott Morrison on Sunday told reporters the hotel quarantine worker had received their first dose of the Pfizer vaccine.

IN THE NEWS:

"There are no risk-free responses when you deal with COVID-19, it is unrealistic and naive to think so ... there are always vulnerabilities," Mr Morrison said.

Chief Medical Officer Paul Kelly said there was a time lag between receiving the vaccine and its protection kicking in, particularly with the Pfizer jab.

"This is not a silver bullet that will fix everything right away," Prof Kelly said.

"There will still be outbreaks, even as we go through this vaccination program."

NSW Health also said anyone who had arrived in NSW from Queensland since March 11 should follow the Queensland government's health advice and avoid NSW aged care homes and hospitals until further notice.

It comes after a doctor last week contracted COVID-19 from a patient at Brisbane's Princess Alexandra Hospital.

Those who have entered NSW and attended the Brisbane venues on the health alert list should immediately self-isolate and contact NSW Health.

"The emergence of these new cases underscores the need for continued community vigilance for any signs and symptoms that could be COVID-19," NSW Health said.

"It is critical that everyone continues to practise COVID-safe behaviours and that people come forward for testing if they have even the mildest of symptoms."

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content:

Australian Associated Press