There were just three new cases found in NSW in the 24 hours, all of them in Western Sydney, detected amid more than 32,000 tests.
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None of the three new cases are linked to the Avalon cluster, and none were in Wollongong.
There were two overseas cases found in hotel quarantine in the 24-hour period.
NSW Premier Gladys Berejiklian said three local cases was "a very positive result" and thanked everyone for having a quiet New Year.
However, she said the pandemic continued to be "an evolving situation" where restrictions could continue to change.
NSW Chief Health Officer Dr Kerry Chant revealed that health investigations had revealed that both the Croydon cluster and Wollongong's two cases had now been linked to the Avalon cluster from a genetic perspective.
However, they are still searching for how transmission to Wollongong and Croydon occurred, with Dr Chant saying Wollongong's Swallowed Anchor bar and restaurant may provide a "missing link".
She said contact tracing had revealed a case from the Croydon cluster and a case from the Wollongong cluster both attended the Crown Street venue on December 19 - meaning NSW Health was now searching for a third party, perhaps from the northern beaches or central Sydney, who may have been at the venue while unknowingly affected.
Late on Thursday night, NSW Health issued an alert for the bar and restaurant, saying anyone who attended there at any time of the day on December 19 must get tested immediately and self-isolate until they receive further advice from NSW Health.
"There may have been a transmission event at that venue," Dr Chant said.
"What we're looking at is whether they were both infected at that time and date. For the abundance of caution, everyone at that venue on the 19th needs to get tested and isolate.
"There may have been a person in that cluster who may have had COVID at that time, who had a link to the northern beaches.
"Other people may have unknowingly been infected."
She thank the restaurant for its cooperation, and said it may turn out that the restaurant was not the missing link, but said it would be an "amazing coincidence" if it was not linked in some way.
The Swallowed Anchor owners Annah Whittaker and Ryan Wilson have temporarily closed their venue and have been working closely with NSW Health.
They posted on social media that it has been "a pretty stressful time for us not only as business owners but as members of the Wollongong community".
Dr Chant again thanked Wollongong residents for turning out in high numbers to be tested, but noted the numbers had dropped off in the city on New Years Eve.
She noted Wollongong had had COVID-19 cases before and had always been "amazing" when it came to testing responses, so she was confident that health authorities would be able to work with the community.
"My call out to the Wollongong community is that you have been amazing over recent days, but this has to be a sustained effort," she said.
"Please continue to come out for testing in the coming weeks so we can be assured we are not missing any chains of transmission in that area."
She also said sewage testing had now become positive in Wollongong, with the state's surveillance program detecting fragments of the virus that causes COVID19 at a sewage treatment plant in Wollongong.
Elsewhere in the state, venues of concern have also been notified in Berala and Smithfield in Western Sydney.
Locations in Eden and Bermagui have also been added to the NSW Health venues list, after travellers from Victoria who had COVID-19 visited venues there.
The positive cases visited the Great Southern Hotel in Eden on Wednesday from 5pm to 6.30pm, and Bermi's Beachside Cafe in Bermagui on Thursday about 9am to 10am.
Dr Chant said people who attended the venues at that time have been asked to get tested and isolate, and NSW Health will provide further advice.
People in the Bermagui area have been urged to monitor for symptoms.
"It is important if you are hearing this and you know anybody within the Bermagui area that you reach to them and make sure that they are aware of the situation," she said.
"We understand that there may be a lot of visitors who have travelled to that part over the festive season."
A full list of venues is available from the NSW Government website at https://www.nsw.gov.au/covid-19/latest-news-and-updates.
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