NSW is not out of the woods yet, Premier Gladys Berejiklian has warned, as she condemned the "brazen" acts of a group who broke lockdown to go to a wedding reception.
Twelve people have been fined over the Pyrmont event on Sunday after police discovered a number of guests and possibly the bride and groom were from the northern beaches - the epicentre of Sydney's COVID-19 outbreak.
"All of us are shaking our heads, absolutely aghast that that has occurred," Ms Berejiklian said on Tuesday.
"Please know that if you do the wrong thing, you will get caught, especially when it is so brazen."
People from the northern beaches are not currently permitted to leave their local area under strict rules to stop the spread of the virus.
NSW Police Assistant Commissioner Mick Willing said on Tuesday more fines would be issued over the reception in Sydney's inner city.
"The bride and groom were involved in it," he said, adding that it's believed they were also from the northern beaches.
Police Minister David Elliott described the breach as a "bastard act".
Meanwhile, there are worrying signs the virus has jumped containment lines.
Three cases have popped up in Wollongong on the south coast, and Sydney's in inner west and north that don't have immediate links to the growing cluster on Sydney's northern beaches.
"We don't want people to think we're out of the woods, far from it," Ms Berejiklian said.
The mystery cases are under urgent investigation, and come on top of three new infections confirmed in the 24 hours to 8pm on Monday.
Those cases are people already in isolation and linked to the cluster, which now stands at 129 cases. The cases were identified from 16,329 tests.
Ms Berejiklian pleaded with residents across the state to get tested in higher numbers.
The new cases come as Sydney approaches New Year's Eve when NSW Police will be out in force to ensure people in Greater Sydney stick to the outdoor gathering limit of 50.
The premier asked Sydneysiders to demonstrate "personal responsibility" and stay COVID-safe on New Year's Eve.
Sydneysiders have been mostly banned from watching the famous New Year's Eve fireworks from the harbour after the foreshores were shut for the first time.
The state government is telling people to stay at home and watch the shortened seven-minute show at midnight to usher in 2021 on television.
The federal government has also warned it could punish backpacker or expatriates who breach of public health orders with deportation.
Federal Immigration Minister Alex Hawke said the government was looking at deporting some of those who attended a large party at Bronte Beach on Christmas Day.
"Under the Migration Act if someone is threatening public safety or health their visa can be cancelled or revoked," he warned.
The northern beaches will kick off 2021 at home after NSW authorities extended stay-at-home orders.
However, small indoor gatherings on New Year's Eve and New Year's Day will be allowed.
Overnight on Tuesday, NSW Health issued alerts for a number of venues in the Sydney CBD and Edgecliff and Bondi Beach in the eastern suburbs and a number of related bus and train routes.
More venue alerts will be issued later on Tuesday.
The state government says 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 remain in place until January 2.
Australian Associated Press