NSW has recorded another sharp rise in Covid-19 cases, with 11 new infections recorded overnight.
There are now 48 infections linked to Sydney's outbreak.
"Since the pandemic started, this is perhaps the scariest period" for NSW, Berejiklian said in this afternoon's press conference. That was partly due to the highly infectious Delta strain of Covid-19 plaguing the state.
However, she said it was "pleasing" that 48,000 people had been tested last night and all but one of the new cases had already been linked to a known cluster.
Appropriate health settings had been put in place to try and bring the outbreak under control, Berejiklian said.
"My level of concern at the moment is medium to high across New South Wales."
Berejiklian reminded residents living in metropolitan Sydney that they were not allowed to leave the city.
"We do not want this spreading to the region," she said.
NSW Chief Health Officer Kerry Chant said she was not yet dismissing the prospect of a snap three-day lockdown.
A short lockdown would work if contact tracers were not able to quickly locate new cases, she said. The current outbreak did still have missing links in the chain of transmission that contact tracers still did not yet know about and that had health officials alarmed.
NSW ministers and MPs in isolation
New South Wales Agriculture Minister Adam Marshall has tested positive to Covid-19, after he was forced into isolation alongside three other Nationals MPs on Wednesday.
Marshall, Trevor Khan, Steph Cooke and Ben Franklin all had dinner together on Monday night at a Paddington restaurant in Sydney's east, and were soon after deemed casual contacts.
NSW Health Minister Brad Hazzard is also in isolation after he was identified as a close contact of a "possible" Covid-19 case who he had interacted with at Parliament House.
Brad Hazzard told ABC Breakfast he had woken on Thursday morning to a message from NSW Health that a case had been detected as a "likely positive" and that he was a "possible close contact".
He believes the suspected positive case is someone who works in the NSW parliament.
"I think it's a message to everybody," Hazzard told the ABC. "If the NSW Health Minister can get a text message during the night and wakes up to that, then obviously we all have a serious issue at the moment with the Delta virus."
Calls for lockdown
Health experts have now repeated calls for Sydney to go into a brief lockdown as the city's outbreak continues to grow.
There are five mystery cases that authorities are trying trace back to known infections.
Professor Mike Toole, an epidemiologist at the Burnett Institute, said contact tracers were now faced with the "critical" task of tracking down the source of those infections.
"If those five cases are still unlinked tomorrow, I think you would want to consider stricter restrictions," he told ABC's Patricia Karvelas.
He added: "I think the next 24 hours will be critical to avert further expansion of this outbreak."
The sharp increase in cases yesterday prompted Berejiklian to announce a raft of new restrictions, including limits on visitors to homes and making masks mandatory at all indoor venues including workplaces and gyms.
Physician and ABC reporter Dr Norman Swan said he believes current restrictions "probably won't" work in slowing the outbreak's spread.
"You see the numbers. I think the numbers are going to be double digit tomorrow from what I can gather," he told The Project. "And that's getting uncomfortably large, uncomfortably large in terms of the contact tracers being able to tie it down and we may well regret not going to a short, sharp lockdown … They don't like using the word, 'lockdown' in New South Wales, but it is pretty close to that now."
Epidemiologist and adviser to the World Health Organisation Professor Mary-Louise McLaws said that the current restrictions should have happened sooner.
She predicted a "big spike" in Thursday's numbers and claimed Sydney will be "very lucky" if it does manage to avoid a lockdown.
"Normally with a Delta, you would see like they did in Melbourne – very fast rise in case numbers and then an incredibly long goodbye – a really long tail," McLaws said. "But we've seen something completely different in Sydney – a very slow increase in numbers … If we get away without a lockdown, then fantastic – I was wrong, fantastic."
Sydney residents must 'abandon non-essential activities'
Berejiklian has urged Sydney residents to "abandon non-essential activities" and not attend social gatherings unless absolutely necessary.
But she said authorities weren't considering a lockdown at the moment as they didn't want to burden citizens with more restrictions unless it was necessary.
"We know basically where the super spreading events have been, we know where the virus is circulating, and we don't want to take any further action than what we have now. This relies on all of us reining in our behaviour, all of us following the health orders that are coming into place," Berejiklian said.
Restrictions in NSW
Restrictions announced yesterday apply to seven local government areas - City of Sydney, Waverley, Randwick, Canada Bay, Inner West, Bayside and Woollahra. The restrictions came into effect at 4pm on Wednesday and will initially last for one week:
• Household visitors will be limited to five guests, including children.
• Masks will be compulsory in all indoor non-residential settings, including workplaces, and at organised outdoor events.
• Drinking while standing at indoor venues will not be allowed.
• Singing by audiences at indoor shows or by congregants at indoor places of worship will not be allowed.
• Dancing will not be allowed at indoor hospitality venues or nightclubs however, dancing is allowed at weddings for the bridal party only (no more than 20 people).
• Dance and gym classes limited to 20 per class (masks must be worn).
• The one person per four square metre rule will be reintroduced for all indoor and outdoor settings, including weddings and funerals.
• Outdoor seated events will be limited to 50 per cent seated capacity.
• Previous public transport capacity limits, represented by green dots, will be reintroduced.