The Deputy Premier told ABC News that the lockdown decision was made at lunch time on Saturday.
"We've always said if we thought this measure was needed we would act quickly and that's why on that advice at lunchtime today we made the decision to go to a statewide lockdown," he said.
Amid confusion over the new lockdown orders, Opposition Leader Chris Minns said the need for "clarity, certainty, and transparency" from the government was needed like never before.
"It is important that announcements that have such a big impact on the people of New South Wales are made from official government and health sources," he told NCA NewsWire.
Earlier on Saturday morning, Berejiklian warned the state was at war with the Delta variant after it recorded 466 new coronavirus cases overnight.
The Premier said in her 11am press conference lockdowns in some areas of concern, such as Western NSW and Armidale, were "likely" to be extended.
In her tweet on Saturday afternoon the Premier said she had received health advice after that announcement.
"Following the press conference today, I received health advice concerning multiple regional NSW areas," she said.
"As such, from 5pm tonight, all of regional NSW will go into a seven-day lockdown. This means the whole state is in strict lockdown."
