There were 18,923 tests reported to 8pm Saturday night, compared with the previous day's total of 31,864.

NSW Health has urged people - especially those in Wollongong, western and south-western Sydney - to continue to get tested with even the mildest of symptoms.

Of the new local cases, five were linked to the Berala cluster, two were contacts of previously reported cases linked to the Avalon cluster, and one is a contact of a previously reported case from Wollongong.

On Sunday morning, Chief Health Officer Dr Kerry Chant thanked the thousands who had come forward for testing, but admitted there were still "missing links".

"We have been dealing with two different strains that have been causing different clusters," Chief Health Officer Dr Kerry Chant said on Sunday morning.

"We had a family group who'd returned from overseas and were transported to a health facility [linked to the Berala BWS].

"There is still, despite intensive investigations, an inability to link Wollongong ... and Croydon Park to the Avalon cluster [although they are genomically linked]."

Dr Chant also said they still don't know who "patient zero" was, who was the person to spark the Northern Beaches outbreak and introduce it to the Avalon RSL several weeks ago.

"It's challenging ... but we may never find that exact link back," she said.

It comes as NSW Health revised their advice for patrons of the Coffee Club in Stockland Shellharbour.

Anyone who attended the cafe for an hour or more on December 27 (from 11:30am-12:45pm) is considered a close contact, and must get tested and isolate for 14 days, despite if a negative result is received.

Dr Chant said they had also contacted around 2000 customers of BWS on Woodburn Road in Berala (who visited on Christmas eve between 12:45pm-9:15pm) to immediately get tested and isolate.

She said it meant tens of thousands of people - who were family and close contacts of those "close contacts" - were also now being told to isolate until they received negative tests.

Meanwhile, masks are now be compulsory in many indoor settings - enforceable with a $200 fine from Monday - across all of Greater Sydney (including Wollongong, the Central Coast and the Nepean Blue Mountains).

People will be required to wear masks when shopping, in shopping centres, on public transport, at an indoor entertainment centre like a cinema or theatre. Places of worship, hair and beauty salons, gaming venues and staff at hospitality venues are also included.

Children under 12 are exempt from the mask wearing rules.

As of Sunday, Shellharbour and Kiama Local Government Areas were not included.

For a full list of where you need to wear a mask, visit the NSW Health website.