A student nurse who worked with patients for up to five days while infectious at two Sydney hospitals has been diagnosed with COVID-19.
The NSW premier, meanwhile, has refused to comment on the prospect of people under 40 receiving the AstraZeneca vaccine, saying only that individuals must first speak with their doctors.
NSW recorded 22 new local coronavirus cases in the 24 hours to 8pm on Tuesday with all of them linked to previous cases, as the state's 14-day virus lockdown continues.
Gladys Berejiklian said initial fears of a dramatic spike in case numbers hadn't been realised but she still expected the numbers to "bounce around".
Of the 22 cases, 11 were in isolation for the entirety of their infectious period. The tally for the outbreak that began on June 16 is now 171.
"Our fears about huge escalation haven't materialised and we certainly want to keep it that way," Ms Berejiklian told reporters on Wednesday.
"If we continue to do the right thing, if we make sure we are following the health advice, then we can get out of this is the time frame we've described."
However, Chief Health Officer Kerry Chant revealed a student nurse was found to be coronavirus-positive after the 8pm deadline.
The 24-year-old Sydney woman worked for up to five days while infectious in Fairfield Hospital's rehabilitation ward and the cardiology ward and general abdominal surgery ward at Royal North Shore Hospital.
One of her household contacts has tested positive to the virus so far.
Dr Chant said the affected wards had been locked down and staff and patients had been tested almost immediately after the diagnosis, including patients who had been recently discharged.
"It's much too early to tell whether we will have any transmission," she said.
Agriculture Minister Adam Marshall is one of the people who contracted the virus amid the outbreak, at a Paddington pizzeria last week.
Mr Marshall said he was keen to get "any" available vaccine rather than wait for the Pfizer jab after Prime Minister Scott Morrison on Monday evening said under-40s can ask their GPs for the AstraZeneca jab instead.
The 36-year-old told the Nine Network on Wednesday his illness had been "debilitating and quite eye-opening" and has compared it to being hit by a bus.
When asked about Mr Morrison's remarks on Wednesday, both Dr Chant and Ms Berejiklian reiterated current federal health regulations and declined to express their view on young people taking AstraZeneca.
They solely said young people should first speak with their GP.
However Ms Berejiklian said NSW Health facilities administering vaccines would continue to give the AstraZeneca jab to only those over 60, as recommended by Australian medical authorities.
The premier also flagged the prospect of new mass vaccination hubs with sites at Lake Macquarie and Wollongong reportedly in the pipeline.
Meanwhile, NSW has tightened the rules for people travelling into the state if they have visited other regions affected by coronavirus.
NSW Health on Wednesday said people from areas in the Northern Territory, Queensland and Western Australia now subject to stay-at-home rules should not travel to the state unless permitted.
From Wednesday, anyone coming to NSW who has been in those areas in the previous 14 days must complete a declaration form.
Wednesday marks the fourth day of a lockdown for people in the Greater Sydney, Central Coast, Blue Mountains, Wollongong and Shellharbour regions.
Ms Berejiklian suggested the transmissibility of the Delta virus strain means some restrictions will likely remain in place even after lockdown.
A number of new exposure sites were on Wednesday listed by NSW Health, the most serious of which being the Bunnerong Gymnastics centre in Matraville on June 23.
Mandatory use of QR code check-ins, meanwhile, will apply from July 12 and be extended to all workplaces, gyms and retail businesses in NSW.