Only 13 of the 27 new cases were in isolation during their infectious period.
The state premier predicted Thursday's case numbers would likely be higher again.
The lockdown for people living in the Greater Sydney region - including the Central Coast - has now been extended until midnight on Friday, July 16.
"This decision wasn't taken lightly," Ms Berejiklian said. "What happens in the next 10 days and beyond is up to all of us... Our police will be out in force, but we also have to take personal responsibility."
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The government's "difficult decision" means students on the Central Coast will join their Sydney peers in online learning when school returns on Tuesday next week.
Schools outside of the Greater Sydney region will resume face-to-face learning.
"It's not because schools aren't safe. They are safe. But what we really need to do in Greater Sydney is reduce mobility," Ms Berejiklian said. "For those parents doing essential work, children will be welcomed onto the school grounds. I also want to thank the regional communities for their patience.
"I appreciate that regional communities like the Central Coast... will be frustrated they have to do another week."
Ms Berejiklian said the continued restrictions across NSW were an "extra measure of safety" to prevent the virus from penetrating the regional areas after several "close calls".
"If we all follow the advice, we will be ok," she said.
Ms Berejiklian said the vaccine was the key to freedom, but the longer lockdown would buy more time to "clamp down" on the virus, and protect the community until the majority of the state's population could be vaccinated.
"The vaccine is the key to keeping our economy open," she said. "What would be far worse is being in a situation where you have to live in and out of lockdown."
NSW Health Minister, Brad Hazzard, said that by Thursday, NSW will have administered a million dose. But the state would like access to more.
There are currently 37 COVID patients hospitalised. Seven are in intensive care - including a person in their 30s, and two are ventilated. Eight are under the age of 35.
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