Concern over COVID cases among people aged 18-20 in Bayside, Georges River and Sutherland Shire

And, police have reiterated the shire is among focus areas for patrols.

There were 112 new locally acquired cases in the 24 hours to 8pm last night.

Premier Gladys Berejiklian said on Monday, "Given where the numbers are, it's not likely, in fact almost impossible to get out of lockdown on Friday".

Of the 112 new cases, 34 were in the community while infectious.

Ms Berejiklian said the number would have to be "close to zero" for the lockdown to end.

NSW chief health officer Kerry Chant said the vast majority of cases were occurring in south-western Sydney, eastern Sydney, with a small number in western Sydney and Nepean - Blue Mountains.

Dr Chant listed suburbs in the Liverpool-Fairfield area where the risk of contracting COVID was greatest.

"Also, we are also seeing cases emerge in young adults in the 18 - 20 age group in the Georges River, Bayside and Sutherland local government area and they largely spreading it... to their closest friends and family," she said.

"So, its crucial that young adults also limit their social interactions at this time and also come forward for testing."

Police Commissioner Mick Fuller said police would continue to focus on areas where there were high numbers of COVID cases.

"We will focus on areas where the virus is and obviously Fairfield is an area of concern as well as Bondi and Sutherland," he said.

Mr Fuller said police would be checking that businesses have QR codes, which are mandatory from today.

"We have seen an improvement with the behaviour of people, particularly wearing masks, and we ask the community to work with us over coming weeks," he said.

Dr Chant revealed there were eight cases of COVID among five households in an apartment block with 29 units in the eastern suburbs.

The source had been identified and health officials were working to move the active cases to special health accommodation and to support the needs of other residents, who must quarantine for 14 days, she said.