NSW Premier Gladys Berejiklian says the latest outbreak in Sydney is the "scariest period" of the pandemic so far for the state.
A further 11 locally acquired Covid-19 cases were announced earlier on Thursday, taking the number of community cases since an unvaccinated limousine driver ferrying air crew tested positive on June 16 to 48.
An additional unlinked case was confirmed overnight, with health authorities frantically trying to curtail the spread of the virus throughout the city with more than 150 exposure sites or transport routes so far identified.
"This is perhaps the scariest period that New South Wales is going through," the premier told reporters.
"It is a very contagious variant."
While Ms Berejiklian said she was content with the current restrictions in place, they were dependant on the entire population doing "the right thing".
Earlier on Thursday, Health Minister Brad Hazzard, who is isolating after being identified as a close contact of a Covid-19 case, said he did not believe Sydney would be placed into lockdown despite growing calls from epidemiologists to do so.
Face masks not foolproof, premier warns
Ms Berejiklian warned residents face masks do not fully protect people from the virus or prevent people from transmitting the virus, particularly with the highly-infectious Delta variant.
"We have had situations where people have symptoms, they are not getting tested and putting a mask on and think they are OK, it is not OK. The mask is simply the fourth line of defence," she said.
Ms Berejiklian said it was vital social distancing, hand sanitising and restricted movement was remembered by residents.
Associate Professor Ben Mullins, an aerosol deposition expert at Curtin University’s School of Public Health, told Yahoo News Australia winter conditions meant aerosols were staying in the air for longer.
Snap lockdown not needed, Chief Health Officer says
Chief Health Officer Dr Kerry Chant said it was time for the virus to "taken seriously".
She warned there was unknown transmission in the community due to three unlinked cases identified, with health teams unaware of how large those chains of infection are.
"That is the reason for the concern, she said.
However she ruled out at this stage a snap, three-day lockdown saying its main purpose is to catch up on a backlog of contact tracing which is not needed currently.
Ms Berejiklian said she believes NSW contact tracers have proven in recent days they are the "best on the planet".
The latest unlinked case is a man in his 40s, joining the hairdresser from Western Sydney who works in Double Bay and the St Charles Primary student as cases with an unknown source.
Ms Berejiklian said she has been cleared to return to work as a casual contact after NSW parliament was rocked by a positive Covid case. She received a negative test result this morning.
On Thursday Victoria confirmed it had recorded a new local Covid-19 case after after a person had returned from NSW. The man in his 60s is isolating as are his close contacts.
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