Outdoor gatherings for greater Sydney will drop from 50 people to 30 and Ms Berejiklian stressed separate groups cannot merge.
“We do ask people to go over and beyond,” Ms Berejiklian said.
We can put all the restrictions we like in place, but if people choose not to do the right thing or exercise good common sense, that is a huge risk to all of us and that’s unfortunately sometimes what happens.”
NSW Chief Health Officer Kerry Chant said the Croydon cluster wasn’t believed to related to several gatherings across the Christmas period.
“That Croydon Park group had a number of family gatherings over a number of days,” Dr Chant said.
Despite the new health order, Ms Berejiklian still promised a relaxing of restrictions from January 3 for residents in the southern section of the northern beaches.
Only half of the 18 new cases were linked to the Avalon cluster in Sydney’s northern beaches, including three mystery cases – two in Wollongong.
Six were from the Croydon cluster and Ms Berejiklian told Sydneysiders to brace for further cases linked to that cluster.
Dr Chant said there were 34 close contacts linked to that cluster.
“I think it just highlights the fact that we can’t have this being seen as a northern beaches local government area issue,” Dr Chant said.
How it’s linked to the Avalon outbreak is unclear.
More than 17,000 people were tested in the 24 hour period, but the Premier still wanted to see those daily rates return to the pre-Christmas levels.
Dr Chant also urged Wollongong residents to get tested.
“It’s critical the community respond with those high testing rates,” Dr Chant said.
A lab error had resulted in health authorities fearing two patient transport drivers had caught the virus from the northern beaches, and not from the infected people they were moving to hotel quarantine.
Dr Chant said the drivers and a close contact were no longer seen as mystery cases.
She urged all Sydneysiders to get tested, not matter how mild their symptoms.
“Don’t think it is the common cold, don’t think it’s another cause,” she said.
“We really need you to go and get tested and remain isolated.”
