Five new cases of COVID-19 which do not have a known source have been identified in NSW in the past day, the health department announced on Wednesday morning.
Chief Health Officer Dr Kerry Chant also warned that there had been "several" other positive test notifications overnight and said she would be updating information about new at-risk venues, especially in the Sydney CBD, throughout the day.
In the official numbers, the state recorded six cases in the 24 hours to 8pm, with one of those detected in an overseas traveller in hotel quarantine.
Two of the locally acquired cases were a man and woman from western Sydney who were household contacts of each other, Dr Chant told said, and the man was a trainee bus driver who worked one shift while infectious.
However she said he had been wearing a mask and had limited contact with passengers, so NSW Health believed the risk of infection was low.
"But we are working with transport to identify people that may have been on that route and we'll provide that in an update," she said.
The other cases were a man in his 60s from south-east Sydney, an unrelated south-east Sydney woman in her 40s, and a woman in her 30s from Sydney.
These cases have led to health alerts for Tattersalls Fitness gym on Pitt Street and the Apple Store Broadway, as well as the building at 300 George Street.
In addition to these five cases, Dr Chant said "we have test results coming in all throughout the night, and we are currently following up cases which we believed are linked [to some of the other cases]".
She said Riverstone High School, Schofields Public School and Wyndham College in Sydney's north-west had all closed due to positive cases detected after the 8pm reporting period deadline.
A Year 12 student was being retested after returning an "equivocal" result yesterday, another teenager returned a result which was positive and the two other children returned negative tests but are being retested as a precaution, she said.
Dr Chant advised people to keep a close eye on the health department website, as she said it would be updating information throughout the day about any new at-risk sites.
NSW Premier Gladys Berejiklian thanked the nearly 26,000 people who came forward for testing in the last 24 hour period, and urged more people with symptoms and in at risk areas to come forward.
"Whilst we have been doing well in the last few weeks, we are not out of the woods yet," she said.