NSW has recorded four new locally acquired cases of COVID-19 and Sydney's Malek Fahd Islamic School is closed after a student was diagnosed with COVID-19.
NSW Health has issued a public health alert for two Sydney venues, including a gym in Sydney's south-west.
Anyone who attended F45 gym in Leppington during certain times over the last fortnight is considered a close contact and has been urged to get tested immediately and isolate for a full 14 days, regardless of the result.
An alert has also been issued for Ali Baba Charcoal Chicken in Auburn. Anyone who attended the venue on Sunday 18 October from 4-5pm is considered a casual contact, and must monitor for symptoms and ge ttested immediately if they develop.
There are four new locally acquired cases of COVID-19 in NSW and one case in a returned traveller in hotel quarantine.
NSW Premier Gladys Berejiklian said three local cases were from the same household and had been isolating.
"NSW Health is working and is confident that there will be an established link to an existing cluster, although that had not yet confirmed," Ms Berejiklian said on Thursday.
There were 14,230 tests reported to 8pm on Wednesday night, compared with 14,382 in the previous 24 hours.
There was another locally acquired case - recorded after the 8pm cut off - which would be included in Friday's numbers.
NSW Health said the first locally acquired case was from southwestern Sydney, and the source of the infection was still under investigation.
The other three contacts were household or close contacts of that case. One of those cases was first reported in a public health alert on Wednesday.
Two of the new cases were students from the Hoxton Park campus of the Malek Fahd Islamic School, in Sydney's west.
The school will be cleaned and closed for 14 days while contact tracing and investigations are underway.
NSW Health said COVID-19 virus fragments had been identified in sewage at treatment plants in West Camden on Wednesday, prompting renewed calls for residents there to get tested. The virus fragments were detected through the state's ongoing sewage surveillance program.
Detection of the virus in sewage samples could reflect the presence of known cases of COVID-19 diagnosed in recent weeks in the areas served by these sewage treatment plants.
However, NSW Health is concerned there could be other active cases in the local communities in people who have not been tested and who might incorrectly assume their symptoms are just a cold.
NSW Health, meanwhile, warned an infected person recently attended a number of venues across Sydney, including restaurants, Westfield Bondi Junction and a trampoline park, and people who visited the sites must be alert for possible symptoms.
The venues include Flip Out Prestons Indoor Trampoline Park in Sydney's west and Jasmins Lebanese Restaurant in Liverpool in the southwest.
Anyone who had attended the venues for at least one hour on Sunday should get tested and self-isolate for 14 days.
The infectious person also visited Westfield Bondi Junction on Saturday, Watsup Brothers kebab shop in Condell Park on Saturday, Ali Baba Charcoal Chicken in Auburn on Monday and Carnes Hill Marketplace on Tuesday.