However, two new cases linked to a western Sydney bottle shop have since been registered, adding to concerns about the Berala cluster.

In the 24 hours to 8pm on Sunday, the state recorded only seven new cases in returned overseas travellers in hotel quarantine. It is the first time daily local cases have been at zero since December 15.

Despite the better news, Acting Premier John Barilaro says testing numbers are still "far too low".

He has implored in western Sydney resident to attend clinics if they have the slightest of symptoms, even if they have been tested previously.

Some 22,275 people were tested in the 24-hour period ending Sunday night, up slightly from 18,923 the previous day.

The government wants to see 30,000 to 50,000 tests each day.

Both cases recorded overnight are linked to the BWS bottle shop in Berala.

One is a man in his 40s who visited the shop on Christmas Eve, and the other a woman in her 40s who has "some association" with the Berala BWS and Woolworths, Chief Health Officer Kerry Chant says.

Anyone who visited the BWS or Woolworths between 12.30pm and 2pm on December 20 is urged to get tested immediately, despite the length of time that has passed and even if they do not have symptoms.

There are new alerts for the Woolworths Berala on December 24, 26, 28 and 31.

NSW Health expects more cases to emerge from the Berala cluster, which now tallies 15.

Tens of thousands of people have been affected by the exposure at the bottle shop.

Most who dropped by the BWS across the Christmas period are now considered close contacts and need to isolate for 14 days even if they only attended the outlet for a short time. They must isolate from household contacts until they receive a negative result.

More than 1000 people attended on Christmas Eve alone.

Meanwhile, Sydneysiders who flout new mandatory mask rules from Monday risk a $200 fine.

Health Minister Brad Hazzard described masks as "absolutely crucial" on Monday.

He says people who oppose masks, like protesters who marched through Westfield Bondi Junction on Sunday, should "stay home or stay outside".

Masks are mandatory in shopping centres, on public transport, in places of worship, hair and beauty premises, entertainment venues such as cinemas and other indoor venues like post offices and banks.

The rule will be in place for some time given the virus risks, Dr Chant says.

"I think people just need to get used to wearing masks," she said.

Although masks are not compulsory in regional NSW, it is still safer for residents to wear them, Mr Hazzard says.

Dr Chant appealed to members of the public to leave enforcement of the mask mandate to police or other officials because some people have medical reasons why they cannot wear them.

"You never know what is behind that for that individual," she said.

People who cannot wear masks should not feel afraid to go about their business, she said.

Mr Hazzard has asked police to exercise discretion in handing out fines to those who ignore the new rules.

Meanwhile, Police Minister David Elliot has described the actions of a southwest Sydney venue operator which allowed up to 700 people to attend a wedding at its site on Saturday as "baffling". The operator will be fined $5000.

The northern part of the northern beaches peninsula remains under stay-at-home orders until at least Saturday. Mr Barilaro on Monday ruled out relaxing the lockdown any earlier.

Australian Associated Press