The official case tally for Thursday was 18 infections, including 13 that were previously announced. A further six cases were recorded after the 8pm cut off and will be included in Friday's numbers.
All but one of Thursday's cases have been linked, Premier Gladys Berejiklian said on Thursday, adding that she was "comfortable that the settings that are in place right now are the appropriate settings".
"Since the pandemic has started, this is perhaps the scariest period that New South Wales is going through," Ms Berejiklian told reporters. "It is a very contagious variant ... please be extra cautious".
Of the five new cases included in Thursday's tally, three have been linked to a party in West Hoxton, near Liverpool in Sydney's west, one is a teenager from Sydney's eastern suburbs who has been linked to the Bondi cluster, and one is a woman in her 20s from Sydney's eastern suburbs who is a close contact of a previously-confirmed case.
Eleven people who attended the 30-person party in West Hoxton have so far contracted COVID-19, including eight announced on Wednesday, after guests were told to isolate and undergo testing.
Five of the overnight cases have been linked to known infections while the source of infection for the sixth case is currently unknown and under urgent investigation.
"We will be doing that backwards tracing and we will go to upstream contact tracing to flush out any unknown chains of transmission," Chief Medical Officer Kerry Chant said.
"We are at a critical phase in the response where we want to see those cases, new cases, and unlinked cases decline."
There are now 36 cases linked to the Bondi cluster.
On Thursday, it was also revealed two Victorian men had tested positive for the virus.
A man, in his 60s, travelled to his daughter's home in Sydney for an event on Saturday before returning to Melbourne the following evening.
He tested positive on Thursday morning, with his boss at Sandringham Dry Cleaners on Bay Road, another man in his 60s, also returning a positive result.
Victoria will designate all of Greater Sydney and Wollongong "red zones" from 1am on Friday.
More locations were also added to the list of coronavirus exposure sites overnight, including Crown Hair in Kings Cross. Anyone who visited the salon between 9am and 5pm on 22 June is being urged to isolate and contact NSW Health.
Agriculture Minister Adam Marshall revealed on Thursday morning he had returned a positive test after dining at a Paddington pizza restaurant on Monday that was later identified as an exposure site.
Health Minister Brad Hazzard has left isolation after he tested negative for the virus following a notification he may have come into contact with a potential positive case.
Ms Berejiklian said she has been deemed a casual contact after returning a negative test on Thursday morning.
She said her parliamentary colleagues were going through screening procedures and no one would be able to reenter the chamber until all necessary assessments have been made.
New restrictions covering Greater Sydney, the Central Coast, Blue Mountains, Wollongong and Shellharbour came into force on Wednesday afternoon.
They include a five-person visitor limit, including children, at home, compulsory face masks in all non-residential indoor settings, a ban on dancing in indoor venues, no standing up while drinking at public venues, a 20-person limit on gym classes and compulsory masks for participants, and the reintroduction of the one person per four square metre rule at all venues, including weddings and funerals.
Outdoor seated events are limited to 50 per cent capacity and people who live or work in the City of Sydney, Waverley, Randwick, Canada Bay, Inner West, Bayside, or Woollahra local government areas are barred from leaving metropolitan Sydney for non-essential travel.