NSW health authorities have recorded four new locally acquired coronavirus cases in the past 24 hours.
A fifth case was also confirmed in an infected traveller who is in hotel quarantine.
The source of one of the locally acquired cases remains a mystery, state health officials said on Thursday.
They have then gone on to infect three household members or close contacts.
"NSW Health is working and is confident that there will be an established link to an existing cluster, although that had not yet been confirmed," Ms Berejiklian said.
One of the four local cases was first reported in a public health alert on Wednesday.
Two of the cases attend Malek Fahd Islamic School at Hoxton Park, which has since been closed for two weeks to undergo cleaning and contract tracing.
It is the highest number of new locally acquired Covid-19 cases in 12 days.
There were 14,230 tests reported to 8pm on Wednesday night, compared with 14,382 in the previous 24 hours.
NSW Covid-19: Traces found in Sydney sewage
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.
Detection of the virus in sewage samples could reflect the presence of known cases of coronavirus 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.
Do you have a story tip? Email: email@example.com.