New South Wales has recorded 38 new community cases of Covid-19 overnight. The source of infection for 12 of those cases remains under investigation.
It is the highest number of new community cases recorded in a single day in more than 14 months and takes Sydney's outbreak to a total of 395.
NSW Premier Gladys Berejiklian said "those numbers are too high" and pleaded with people to stop visiting extended family.
"When we talk about providing care or compassion, we are talking about one person visiting someone who might be isolated, dropping off essential services or goods," she said. "We are not talking about visiting extended family members, we're not talking visiting friends. Data over the last few days shows this is how the virus is spreading."
Berejiklian said the "saddest message out of all of that is that people with the virus are passing it on to those they love the most" like grandparents.
"We need to be stern about this. We need less movement to get those number of exposures down. We don't want to prolong the lockdown, we don't want to see Sydney or NSW going in and out of lockdown until we have the vast majority of our population vaccinated."
She added: "It is up to all of us to step up, as difficult as it is."
In NSW there are currently 40 Covid-19 cases admitted to hospital, with 11 people in intensive care, three of whom require ventilation.
Berejiklian said that while NSW had "always been bold and courageous in terms of our attitude and how we deal with Covid-19", people had to accept that the "Delta [variant] is very different to everything we have seen before".
Asked whether the outbreak's trajectory might mean the state "won't necessarily come out of lockdown" as planned next Friday, Berejiklian was non-committal.
"What is important is all the experts have said if every single person does the right thing, that we can get to where we need to go at the end of the three-week [lockdown] period," she said.
"That is a big ask because we know that unfortunately, unintentionally at times, people don't do the right thing, so it's really important for all of us to have equal responsibility."
Dire warnings of wider outbreak
Australian infectious disease experts are warning the country "could end up with a situation like India" if the Delta variant is allowed to run rampant throughout the Sydney community.
It comes after New South Wales Health Minister Brad Hazzard suggested on Wednesday that the state might never control its current outbreak, and be forced to accept community spread of the virus "for good".
The Greater Sydney lockdown was extended by a week after case numbers on Wednesday were "higher than anticipated".
Hazzard said if people don't do the right thing over the coming days, "then at some point we're going to move to a stage where we're going to have to accept that the virus has a life which will continue in the community".
Speaking to ABC Breakfast on Thursday, Raina Macintyre from the Kirby Institute said letting the virus continue to spread would be "really risky".
"I think for Australia, for NSW, that's a different proposition to countries that have high vaccination rates and high levels of disease. We've got virtually no immunity in the community because very few people have been fully vaccinated, and very few people have been infected," she said.
"So we are absolutely susceptible. If we let it spread in Sydney, it could impact the whole country and we could end up with a situation like we saw in India in March and April.
"We can't afford to relax until we've got the vaccination rates high."
Expert wants longer lockdown
University of Melbourne epidemiologist Tony Blakely has slammed NSW's lockdown as "ridiculous", saying it isn't harsh enough.
"If you want to get your lockdown over soon, do it properly," he told Seven's Sunrise.
"If you muck around, this will just keep on going. You can't just do a half-hearted one and expect it to last a week, you have to do it properly, otherwise you'll be doing lockdown for ages."
Blakely said it was "concerning" that NSW was not planning to extend the lockdown even longer.
"There seems to be this idea we're going to end this Friday no matter what," he said.
"If you do that, it will blow up and NSW will be a hell of a mess between now and when vaccination coverage gets to 50 per cent, and it will probably take the rest of the country down with it. It's that serious."
Blakely said if "common sense prevails", the lockdown will continue.
"But everybody needs to understand, if you want the lockdown to be done with quickly, do it well," he said.