Mandatory mask-wearing has been extended by a week for Sydneysiders as the number of cases linked to the Bondi cluster reaches 21.

Sydneysiders will mask up for an extra week and wait for extra vaccine doses while hoping the number of mystery cases in NSW does not surpass one.

The state recorded 10 new locally acquired cases of COVID-19 on Tuesday - including an eastern suburbs child - bringing the number of cases linked to the Bondi cluster to 21.

NSW Premier Gladys Berejiklian says masks will remain compulsory until midnight on June 30 on public transport and in most indoor settings for people in Greater Sydney, the Blue Mountains, the Illawarra and Shellharbour.

"It is only when you are eating or drinking indoors at a venue that you can't or shouldn't wear a mask," she said.

When asked whether a snap lockdown was likely for Sydney, she said she had a "degree of confidence" in the situation because all but one of the new cases were linked to existing cases.

"If we suddenly have a number of unlinked cases and if we suddenly have them outside the geographic region they are concentrated in, that will obviously adjust the health advice and we will respond to that," the premier said.

All of the new cases except for two were already in isolation when tested and all of the cases but one, a student at St Charles Catholic Primary School in Waverley, were linked to existing cases.

Sydney Catholic Schools confirmed the Year 3 student had tested positive for the virus and the school had closed for the final three days of term two while it's cleaned.

Chief Health Officer Kerry Chant said it wasn't yet known how the child contracted the virus and health officials were working to develop a plan for the 365 children to be tested.

NSW Health has also ramped up its advice around the original infection site at Westfield Bondi Junction and is asking anyone who was there - including the car park - at any time between June 12 and 18 to get tested for COVID-19.

Only people with symptoms and those who have been to specific exposure venues at the listed times need to test and isolate.

Five new cases were detected in testing in the 24 hours to 8pm on Monday - two of those had already been announced and both people tested positive while in isolation.

An additional seven cases were diagnosed after 8pm on Monday and will be included in the official tally for the next 24-hour period.

The three new cases reported in the period to 8pm on Monday included a woman in her 60s in the Illawarra and a woman in her 40s from Sydney's northern suburbs, who had both been in isolation as they were close contacts of previously reported cases.

A woman in her 20s from Sydney's eastern suburbs who works at Bondi Junction also tested positive.

Testing numbers were up to 28,645 by 8pm on Monday night compared to 25,252 the previous day.

The extension of mandatory mask-wearing for Sydneysiders was welcomed by the union covering retail, fast food and warehouse workers.

"Retail workers have done an incredible job on the frontline of the pandemic, working day in and day out to keep up an essential service, and they deserve to be protected," SDA NSW and ACT secretary Bernie Smith said.

Meanwhile, the premier said an extra 50,000 doses of the Pfizer COVID-19 vaccine will be distributed to NSW over the next three weeks.

The premier also flagged she was in the process of mandating the use of QR codes at all retail outlets. New venues have been added to the growing list of exposure sites identified across more than a dozen suburbs.