However, the State Government has declared Sydney’s northern beaches local government area a “high community transmission zone”.

People are being asked to notify authorities if they visited the area since December 11 and, if so, immediately get tested for COVID-19 and quarantine for 14 days at home.

South Australia has also reinstated the cross-border travel application process – the online approval form – for anyone who is travelling from NSW into SA.

State emergency coordinator Grant Stevens said the form would ask people to disclose if they visited Sydney’s northern beaches local government area since December 11.

He said people in South Australia who visited the Avalon RSL or the Bowlo bowling club since December 11 must immediately quarantine at medi-hotels.

South Australians who have visited those two locations but are yet to travel back into SA will not be allowed into the state.

SA Police will not reinstate its border check points on roads between SA and NSW for now, but it will have a “significant presence” at the Adelaide Airport.

SA Health this morning issued an alert telling people who recently travelled to NSW and visited the cluster hotspot locations on the date and time listed on the NSW Health website to immediately self-quarantine for 14 days, starting on the last day they were at the site.

They must also get a COVID-19 test immediately and again on day 12 of self-quarantine.

Some people may be asked to have additional tests.

SA Pathology is setting up a testing clinic at Adelaide Airport to ensure people get tested as quickly as possible.

Marshall this morning said that SA would not follow WA and Queensland by tightening its border restrictions with NSW.

“We’ve had excellent information that’s flown through from NSW Health this morning,” he said.

“We’re going to monitor it over the next couple of days, but we won’t be immediately closing the border with New South Wales.”

He said the cluster’s two main “super-spreader” sites had QR codes in place for “a long period of time”, giving health authorities here confidence that NSW could easily “put a net over the cluster”.

He said by keeping the state’s border open to NSW, SA would not comprise its COVID-free status, after only recently combating the Parafield cluster.

“At the moment we are satisfied with the excellent work that New South Wales Health are doing,” he said.

“If we find that there have been further clusters developing in other non-link cases then that will be a very different situation and obviously we’ll take corrective action.

“We won’t be making any knee-jerk reactions – we’ll be listening to New South Wales health, we’ll be looking at their data and we’ll be making informed decisions that protect our state.”

Chief public health officer Professor Nicola Spurrier said that the cluster was “localised at the moment”, meaning health authorities here were confident that they could keep the border open.

“The public health basis behind this decision is that it has.. been picked up very early and it’s very localised at this point,” she said.

Spurrier said authorities were currently trying to determine whether anyone who visited yesterday’s test cricket match at Adelaide Oval had been to Sydney’s northern beaches recently.

She encouraged people who are attending the remaining test cricket matches at Adelaide Oval to wear masks when they are queuing or travelling to and from their seat.

But authorities are not expecting any changes to South Australia’s restrictions “at this stage” in the lead-up to Christmas.

NSW authorities today announced they had sourced the cluster back to a strain from the United States that might have entered Australia early this month, after 15 new local cases of COVID-19 were recorded in the 24 hours to 8pm last night.

One case was uncovered in a person who had since travelled to Queensland.

Another 10 people were confirmed virus-positive after 8pm on Thursday.

Two cases on the northern beaches had been confirmed in the 24 hours to 8pm on Wednesday.

The cluster includes a residential aged care worker and a man who recently performed in a band at three RSL clubs.

The northern beaches peninsula has entered a quasi-lockdown, with NSW Health asking about 250,000 people in the Northern Beaches Local Government area to stay at home and not leave the for the next three days. Aged care facilities in the area have been shut to visitors.

NSW Premier Gladys Berejiklian has implored northern beaches residents to only leave home for essential reasons over the next few days.

“The harder all of us work together, the better Christmas we’ll have,” she said.

It comes as the WA Government announced that anyone travelling from NSW into the state must self-isolate for 14 days.

Anyone who enters Queensland and has been on Sydney’s northern beaches since December 11 must get tested and self-isolate for 14 days since their last visit to the region. From Saturday, all people who have been on the northern beaches and want to enter Queensland will be forced into hotel quarantine.

The other states have also tightened the screws on their border arrangements with NSW.

But the Federal Government urged the states and territories to exercise some restraint in relation to border closures.

Finance Minister Simon Birmingham said SA had a “reasonable and sensible” response to the Avalon cluster.

“I would urge that states do work in ways that are proportionate to the circumstances and do act in a manner that gives New South Wales the chance to be able to overcome this cluster,” he said.

“We’ve got to back those systems that have proven to be so successful to date rather than jump to actions that will undermine the economic recovery and hurt in terms of jobs, livelihoods and indeed family reunions at this time.”

His mid-year economic update is predicated on borders staying open.

South Australia recorded no new coronavirus cases today.

-with AAP