A total of 23 cases were detected in the 24 hours to 8pm on Friday, including the 10 that were reported yesterday.

Of those cases, 21 have been linked to the Avalon cluster while two are under investigation but are suspected to be linked to the same cluster. Another seven cases were detected in hotel quarantine.

As a result of the outbreak, NSW Premier Gladys Berejiklian imposed heavier restrictions on the Northern Beaches local government area.

"Based on the likelihood that we're going to expect to see a repeat of those numbers across this 24 hours ... we are going to put in health orders for the Northern Beaches from 5 o'clock today to essentially go back to the restrictions people experienced in March," Ms Berejiklian said.

Northern Beaches residents will only be able to leave their homes for work, compassionate grounds, shopping and exercise. The order will be in place until midnight on Wednesday.

"That is to give all of us a chance to have a better Christmas than what would otherwise occur," she said.

Greater Sydney residents have been urged to limit non-essential activity, and Ms Berejiklian warned harsher restrictions could be introduced for the city tomorrow.

All NSW residents have been urged to monitor the NSW Health website as hotspot locations are detected and uploaded to the page.

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