A 25-year-old man will face court accused of assaulting a Sydney shopping centre security guard then stabbing a passerby, after the woman he was with was asked to wear a mask.

The man was at the shopping centre at north-western Windsor on Tuesday night with a woman and two children when the guard asked the woman to put on a mask.

Police have been told he approached the 59-year-old guard shortly after and punched him several times.

A 53-year-old man intervened and the younger man stabbed him in the leg, police say.

The customer and guard restrained the man until police arrived.

The case has been adjourned until January 25 after the man did not appear at Penrith Local Court on Wednesday and did not apply for bail.

NSW had one new locally acquired coronavirus case on Wednesday, as authorities warned virus restrictions – including mandatory masks in public indoor spaces such as shopping centres – were likely to remain for weeks.

NSW authorities say masks are likely to remain mandatory for weeks. Photo: Getty

Chief health officer Kerry Chant said it would probably take up to four weeks to “mop up” Sydney’s Berala and Avalon clusters.

“The more we can adopt those COVID-safe practices, those practices of wearing masks indoors, getting tested as soon as possible with the most minimal of symptoms, maintain that physical distancing, this will all mean that even if we don’t recognise a case, it’s less likely to transmit to multiple people,” she said.

“It is almost a time to re-double our efforts as we try to get to no community transmission as soon as possible.”

There were more than 20,600 COVID tests in NSW in the 24-hour reporting period. That is well up from Monday’s figure, which prompted authorities to plead for more people to get tested.

Premier Gladys Berejiklian also urged residents to “stay on high alert”.

“We don’t want to see any super-seeding events, we don’t want to see super-spreading events,” she said.

“We don’t want an occasion where someone who may not know they have the virus unintentionally passes it on.”

The sole case in the 24 hours to 8pm on Tuesday was a child who is a close contact of a previously confirmed case linked to the Berala cluster in western Sydney. It now numbers 28 people.

Six COVID-19 cases were uncovered in NSW hotel quarantine.

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Ms Berejiklian also confirmed two mystery cases that emerged in Sydney this week – a COVID-positive man, who presented to Mount Druitt Hospital with respiratory symptoms, and his partner – are linked to the Berala cluster.

She also backed her state’s contact tracing teams, saying their work enabled the government to make decisions that didn’t place “unnecessary burdens” on residents, such as keeping interstate borders open.

“We’ve always said in NSW – and we adhere to this policy – that we don’t want our citizens to bear any extra rules a day longer than they need to,” she said.

“If the health advice suggests that a day is a particular time to ease restrictions then, of course, we’ll do that.

NSW has one COVID patient on a ventilator in intensive care.

Public health alerts remain for dozens of hotspots, including a shopping centre in Warriewood, a post office in Hurlstone Park and a workers’ club in Blacktown.

A casual-contact alert was issued on Tuesday night for The Groomsmen Barber Shop inside the Warriewood shopping centre.

Meanwhile, the ACT and Northern Territory have lifted travel restrictions for residents of the Central Coast, Wollongong and some parts of greater Sydney.

-with AAP