Sydney is bracing for a ‘significant increase’ in coronavirus numbers after a mystery case at a primary school and a retail worker’s positive test.

Sydney Catholic Schools has confirmed a year three student returned a “preliminary positive” COVID-19 test on Tuesday.

St Charles Catholic Primary School in Waverley closed on Tuesday. All students were sent home in a staggered departure as authorities stepped up their hunt for the source of the girl’s infection.

NSW Premier Gladys Berejiklian has so far resisted imposing a lockdown to deal with the expanding Bondi cluster, which hit 21 infections on Tuesday. However, she has refused to rule out the measure entirely.

“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,” Ms Berejiklian said.

She said she had a “degree of confidence” in the situation because all but one of Tuesday’s infections were linked to existing cases.

There were five new infections in the outbreak in the 24 hours to 8pm Monday. Two had already been reported – both close contacts in isolation.

Tweet from @NSWHealth

An additional seven cases were detected after 8pm on Monday, and will be included in Wednesday’s numbers.

Six of those were already in isolation when they became infectious. The seventh – the primary school girl – has been deemed a mystery case.

Earlier, chief health officer Kerry Chant said the school was working with health officials to develop a plan for the 365 students to be “discharged home to their parents” and tested.

Tweet from @NSWHealth

The other case causing most concern to health authorities is one from Tuesday’s official count – a woman in her 20s from Sydney’s eastern suburbs who works at Westfield Bondi Junction.

Dr Chant said neither the student nor the worker were in isolation when they tested positive, sparking transmission fears.

Ms Berejiklian said authorities were expecting significantly more infections in the coming days as close contacts get tested.

“That shopping centre has generated a number of cases and we want to make sure we have captured everybody. It could involve thousands of extra people getting tested now,” Ms Berejiklian said. 

“We have the capacity for that to happen and we urge people to come forward. The high number of tests we have, the better number it will be to make sure we haven’t missed any strains of community transmission.”

On Monday, Dr Chant said CCTV footage indicated the virus had been passed between two shoppers who briefly walked past each other.

“They are clearly facing each other but it is literally someone moving across from each other for a moment, close, but momentary,” she said.

NSW Health has also asked anyone who was in Westfield Bondi Junction – including the car park – at any time between June 12-18 to get tested.

COVID-19 measures imposed for Sydney, which were originally set to end at midnight Wednesday, have been extended until at least June 30 after the spike in cases on Tuesday.

Masks remain compulsory on public transport and have become mandatory in most indoor settings for people across all of 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,” Ms Berejiklian said.

“In every other circumstance, if you live or are in Sydney, you must wear a mask for another week beyond Wednesday midnight.

“Unfortunately, a number of people who have contracted the virus have done so in a very fleeting way,” she said.

• An updated list of NSW exposure sites can be found here.

Health authorities will also make QR check-ins mandatory at all shops – a measure taken by Victoria several weeks ago.

NSW Health Minister Brad Hazzard said the Delta variant of COVID-19 was a “gold medallist” in jumping from one person to another and he encouraged people to use QR codes.

New venues have been added to the growing list of exposure sites identified across more than a dozen suburbs.

Travel doors reopen to ‘on track’ Victorians

Meanwhile, in Victoria, no new cases were detected in the 24 hours to midnight on Monday.

Chief health officer Brett Sutton signalled a further relaxation of the state’s COVID rules was likely this week, but it was still too early to go into the detail.

“We’re absolutely on the right track, I also have strong expectations we can go that next step, both metropolitan Melbourne and regional Victoria,” Professor Sutton said.

“We are looking to do as much as we possibly can and part of having these couple of days for that further assessment is to go as far as we possibly can in making those changes.”

Tweet from @VicGovDH

While some virus measures remain, interstate travel has again become an option for Victorians.

Tasmania and the Northern Territory welcomed travellers from greater Melbourne overnight. Some bans remain for people who have been to specified “hot spots” in Victoria at certain times.

Queensland and South Australia are preparing to welcome Victorians back from Friday.

Even a trip to New Zealand is back on the cards, with the trans-Tasman bubble to return for Victorians from midnight Tuesday.

-with AAP