Sydney's Northern Beaches placed under lockdown.

Residents of Sydney's Northern Beaches will go into lockdown, as authorities race to contain a cluster of COVID-19 cases in the region.

NSW recorded 23 locally acquired cases of the virus in the 24 hours to 8pm Friday, including the 10 announced earlier in the day.

Speaking to the press, Premier Gladys Berejiklian said 21 of the new cases have been linked directly to the cluster stemming from the suburb of Avalon, and the two under investigation are also suspected to be related.

There were 12,374 tests reported to 8pm last night, compared with 7,531 in the previous 24 hours.

There are more than 300 COVID-19 testing locations across NSW. To find your nearest clinic visit https://t.co/3q77lQTr7P or contact your GP.

— NSW Health (@NSWHealth) December 19, 2020

The new restrictions for the Northern Beaches will come into effect at 5pm Saturday and will last until midnight Wednesday. 

During that period, Northern Beaches residents are only permitted to leave their home for essential purposes including work, exercise, shopping, medical care and to care for vulnerable relatives.

The premier also strongly urged people in Greater Sydney to cancel non-essential activity over the same period.

"We are asking you to do this in good faith," she said. "If you are planning a night out tonight, we ask you to consider changing those plans and staying at home. We want people to stay at home tonight and the next few nights so that we can ensure the virus does not spread if there are any fragments of the virus outside of the Northern Beaches, and we also want to make sure that we give all of Sydney the best chance we have to have a good Christmas."

The premier also flagged the possibility of wider restrictions if the virus spreads.

"We will be considering today after consulting obviously the relevant people, whether this time tomorrow we do revert back to some restrictions in Greater Sydney," she said. "But we are still considering that. I just want to put everybody on notice that that is a possibility and that will depend on the health advice sent to us during the course of the day."

Though cases are currently localised to the Northern Beaches, NSW Health has issued a lengthy list of venues visited by confirmed cases across Sydney, with warning periods ranging from December 11 to December 16.

They include numerous places around the Northern Beaches, but also Cronulla RSL Club, Westfield Bondi Junction, a hair salon in Turramurra and Lane Cove, a Woolloomooloo restaurant and other venues and transport routes around Sydney.

A full list of the affected locations is available via the NSW Health website.

Anyone in the Northern Beaches LGA has also been asked today to wear a mask when indoors for at least the next 72 hours, excepting your own home.

Confirmed cases of COVID-19 have visited a number of locations around Sydney.

— NSW Health (@NSWHealth) December 18, 2020

Genomic sequencing has connected the cluster to a US strain of the virus, which may have entered NSW in a returned traveller in early December.

That traveller has never left the hotel quarantine system, meaning the connection between that case and the Northern Beaches remains unclear.

As the situation has evolved over the past few days, other states have enacted pointed restrictions prevent the cluster jumping borders, with more barriers for NSW residents erected by Western Australia, Victoria, Queensland, Tasmania and the Northern Territory.

Anyone who enters WA from NSW will be forced into 14 days of self-isolation, and people who have been in the Northern Beaches will not be able to enter Queensland without quarantining. (See below for further details.)

On Friday, Victoria introduced a permit system for all people travelling from NSW into Victoria, which came into effect at midnight.

The state will operate under a "traffic light" system. Hotspots — including the Northern Beaches — are considered a "red zone" and those from these areas will not be permitted to enter. If they do arrive, they will be forced into hotel quarantine.

Greater Sydney is being classified as an "orange zone", and residents are being encouraged to get tested regardless of symptoms and to self-isolate until they receive a result. And the rest of NSW has been classified as a "green zone".

Further details on border rules are available on the Health Direct website.

Queensland keeps NSW border open; no new cases recorded.

Queensland will keep its borders open despite a traveller from Sydney's Northern Beaches sparking a coronavirus scare in the state.

Chief Health Officer Jeannette Young said authorities were tracing the contacts of the woman who arrived in Brisbane on Virgin Airlines flight 925 at 9.30am on Wednesday before visiting a number of locations on the Sunshine Coast. 

The woman took a COVID-19 test at Prince Charles Hospital on Thursday, which came back positive, before returning to NSW.

UPDATE: @queenslandhealthnews has expanded the list of locations visited by a confirmed case. If you have been to any of these places at these times and develop any symptoms, you should isolate immediately and get tested.#covid19auhttps://t.co/IadaAsBvVt

— Annastacia Palaszczuk (@AnnastaciaMP) December 18, 2020

In response to the NSW cluster, Queensland imposed a 14-day hotel quarantine on all arrivals from Northern Beaches from 1am on Saturday.

Anyone from that part of Sydney already in the state has also been ordered to self-isolate for 14 days.

Cutting short her beach holiday, Premier Annastacia Palaszczuk stressed on Friday that Queensland's borders would remain open to other travellers.

"I just want to give people that sense of security, in terms of we are following practices that other states and territories are also (practising) at this stage," she told reporters.

"So I just want to alleviate people's concerns there."

However, the premier urged Queenslanders to reconsider travel to the Northern Beaches and urged Sydneysiders from the peninsula not to visit her state.

"This is of concern, when the NSW premier says she's on high alert, we are on high alert as well," Ms Palaszczuk added.

Deputy Police Commissioner Steve Gollschewski said passengers on every incoming flight were being checked and cars with NSW registration plates randomly stopped at the border.

He said anyone from the Northern Beaches must fill out a declaration before travelling to Queensland from Saturday.

Officers will also be checking on visitors from that part of Sydney to make sure they're self-isolating.

No new cases were recorded in the state on Saturday.

Saturday, 19 December – coronavirus cases in Queensland:

• 0 new cases
• 10 active cases
• 1,232 total confirmed cases
• 1,411,993 tests conducted

Sadly, six Queenslanders with COVID-19 have died. 1,214 patients have recovered.#covid19 pic.twitter.com/O0D7JTpXqU

— Annastacia Palaszczuk (@AnnastaciaMP) December 18, 2020

SA leaves border open to most Sydneysiders.

South Australia has left its border open to travellers from NSW but warns it won't hesitate to act if Sydney's COVID-19 cluster continues to expand.

However, people from the city's Northern Beaches and two other suburbs will face immediate restrictions with some being forced into hotel quarantine and others into home isolation.

Police Commissioner Grant Stevens says Sydney's northern peninsula has been declared a high community transmission zone. 

He says people who recently travelled to SA and had visited Avalon RSL and Avalon Bowlo will be placed into hotel quarantine.

It's unclear at this stage how many, if any, that will involve.

Anyone else who visited those two locations who is still planning to travel to SA will not be permitted to enter.

Anyone travelling from the wider Northern Beaches area will be required to self-isolate for 14 days and get tested. The same applies to people who have been in Sydney's Penrith or Lavender Bay since December 11. 

The State Coordinator and Police Commissioner Grant Stevens today announced people who have travelled to SA from particular areas in NSW are required to immediately self-quarantine for 14 days & seek COVID-19 testing. For information visit https://t.co/wkKuWkCu3K pic.twitter.com/wMcLCCbEiH

— South Australia Police (@SAPoliceNews) December 18, 2020

Mr Stevens said he had a strong sense NSW officials were moving "aggressively" to contain the cluster.

"But this is pandemic, it is unpredictable and we have an obligation to make hard decisions and we will do that if we need to," he said.

"If this cluster grows beyond the Northern Beaches and is seen to have spread far more widely through the NSW community, that is certainly something we will have to take into account."

South Australia has also reinstated a requirement for all people coming from NSW to complete an online border travel application.

No new virus cases were reported in SA on Friday and the state has no active infections.

SA is now less than a week away from declaring its recent Parafield cluster officially over.

Authorities consider two incubation cycles, or 28 days, the necessary timeframe before an outbreak is declared eliminated.

— With AAP

Feature Image: Getty.