Christmas hope as NSW records 15 new coronavirus cases after record testing blitz

Sydney's battle to save Christmas has received a massive boost after a record-breaking testing blitz uncovered only 15 new cases today.

Even as Queensland dealt a big blow by announcing it was reinstating its hard border with NSW, the local fight to contain the spread of the virus to the Northern Beaches looked hopeful.

After 38,578 tests, the 15 new cases were only half of the number of the day before and all have been linked to the Avalon cluster, which has now grown to 83. Eight of those new cases were already in quarantine.

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"There is no doubt that we're pleased with what we've seen today, but one thing I've learned during the pandemic is that things are very volatile," Premier Gladys Berejiklian said.

Linking all cases to the Northern Beaches gives hope that the virus isn't spreading in other parts of the city, but with positive cases visiting more than 100 venues across Sydney and into regional areas there are worryingly clusters forming outside of the peninsula.

The Belrose Bunnings, Newport Coles, Dan Murphy's in Mona Vale, and multiple supermarkets, shopping centres, hotels and cafes have been added to the list of hotspots.

"Whilst we have a strong focus on the Northern Beaches it is important that we have no complacency across the Greater Sydney region," NSW Chief Health Office Dr Kerry Chant said.

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The fate of Christmas hangs delicately in the balance — whether the Northern Beaches will be forced to celebrate in lockdown and if the rest of Sydney can have up to 10 guests will depend on how the numbers fall over the next few days.

Ms Berejiklian said she expected more detail by Wednesday.

"I appreciate how frustrating it is and I'd love to be able to tell everybody today what Christmas might look like in NSW or the Northern Beaches, but we're not in a position to do that yet," she said.

READ MORE: Can I still travel to regional NSW?

Patient Zero is still a mystery but international flight crews have been to blame for the last two outbreaks in Sydney.

From Tuesday, those crew members will be treated as return travellers in NSW, met by police and soldiers and forced to stay in one of two quarantine hotels upon arrival.