The Avalon cluster on Sydney's northern beaches, which erupted earlier this month, generated another nine cases in the 24 hours to 8pm on Tuesday. The case load in the hot spot now stands at 138.

Another group of six infected people - dubbed by health experts as the Croydon cluster - was also revealed on Wednesday.

It includes three adults and three children from the same extended family who gathered for several events over a number of days.

The six are from three different households and some live outside the Croydon area. Authorities have not yet found a link to the Avalon cluster.

"The Croydon cluster is concerning because there's no established link ... all the other cases, there is some crossover with venues or regions that we've identified as a concern," Premier Gladys Berejiklian said on Wednesday.

"We anticipate that because of the nature of that extended family's movements, there will be more cases from that cluster."

Due to the overnight growth in cases outside the northern beaches, tighter restrictions for New Year's Eve and beyond will be enforced.

Household gatherings across greater Sydney - which includes Wollongong, the Central Coast, Nepean and the Blue Mountains - will be limited to five people inside, down from 10, and 30 outdoors, down from 50.

Additionally, authorities are investigating three other COVID-19 cases involving two people from the same household in Wollongong and another in northern Sydney.

Close-contact alerts were on Wednesday issued for two venues inside Bankstown Sports Club - including the La Piazza eatery - on December 28, as well as a nail salon and hair salon in Bass Hill on December 24.

People who attended those venues on those dates must get tested and self-isolate for 14 days regardless of the result.

Other casual-contact alerts were issued for pharmacies in Bankstown, Liverpool and Katoomba in the Blue Mountains.

Earlier alerts were released for a restaurant at the Sydney Opera House, as well as the Santa Claus photo booth at Burwood Westfield, Officeworks at Punchbowl and the Coffee Club cafe at Stockland in Shellharbour.

The Wollongong cases on Tuesday also sparked close-contact health alerts dating back to December 27 for two Greek Orthodox churches in the city - St Nektarios Church and The Holy Cross Church.

Chief Medical Officer Paul Kelly told reporters he supported the restrictions.

"NSW Health right throughout this pandemic have been our poster people, if you like, in relation to their contact tracing," Dr Kelly said.

"It's always amazing how quickly they get onto things and how quickly they work through what are sometimes very complex chains of transmission and get very detailed genomic analysis."

Elsewhere, an additional nine $1000 fines have been handed to guests at a Pyrmont wedding after numerous attendees, including the bride, travelled from the northern beaches.

Police Minister David Elliott said the 21 breaches relating to the incident were disappointing.

Sydneysiders are mostly banned from watching the city's New Year's Eve fireworks from the harbour on Thursday, with the foreshore fenced off.

To avoid "super spreading events", Ms Berejiklian said the five-person rule for indoor gatherings will remain beyond New Year's Eve, until all strains of virus transmission have been identified.

Stay-at-home orders applying to northern beaches residents north of the Narrabeen Bridge will continue until at least January 9. A lockdown for the peninsula's southern zone will be in place until January 2.

Australian Associated Press