The SA Government has announced all residents returning from Victoria will be required to take a coronavirus test within 24 hours of their arrival, and wear face masks when coming into contact with others.
A hard border closure with Victoria was imposed at midnight, preventing anyone other than South Australian residents and essential travellers from entering.
SA Premier Steven Marshall today said that all travellers from Victoria would be required to self-isolate for 14 days, submit for a coronavirus test and another one 12 days later.
"Any South Australians that are returning will be required to undertake a test within 24 hours of crossing the border," Mr Marshall said.
"Even if they get a negative result, they are still required to complete the full 14 days of isolation.
"As a further precaution, we will be making a phone call to all of those returned South Australians within 24 hours to check that test has been undertaken.
Travellers who arrive at checkpoints at the border or at the airport will be provided with free face masks, which they will be required to wear when leaving isolation for testing.
"They will be presented with three face masks which they must wear when they are coming into contact with any other people," the Premier said.
They will also be provided with pre-signed forms for testing, allowing them to go directly to a COVID-19 clinic without needing a GP referral.
Mr Marshall said SA Pathology would also begin a "testing blitz", with anyone who had been to Victoria in recent weeks urged to present for testing, whether or not they have experienced coronavirus symptoms.
"We will be starting a testing blitz in South Australia, effective immediately," Premier Marshall said.
"We are asking all people who have entered Victoria in recent weeks to present themselves immediately for testing for the COVID-19.
"Even if people do not have symptoms we are asking them to present themselves to make sure we can look at every single possibility."
SA Health repeats plea to those with symptoms
The Victorian Government imposed stay-at-home orders across metropolitan Melbourne overnight, affecting more than five million people there.
"What's occurring there is just a blunt reminder to every South Australian that we can't rest back on our laurels [and] we can't be complacent with regards to this disease," Mr Marshall said.
"Businesses only opened up in Victoria a few weeks ago and now they're being forced to close down.
"We don't want that situation in South Australia."
Mr Marshall said more than 300 people crossed into South Australia over the Victorian border between 6:00pm yesterday and midnight, when the hard border came into effect.
After earlier raising it as a possibility, Police Commissioner Grant Stevens said the Australian Defence Force (ADF) was now assisting with border control efforts.
"We have ADF support in our police operations centre starting today and also at Mount Gambier, and they'll be helping with the coordination of ADF resources," he said.
"We are bringing in Defence Force personnel, inducting them and then teaming them up with police officers to support our efforts to keep the borders closed."
SA Chief Public Health Officer Nicola Spurrier again urged anyone in South Australia with respiratory or cold-like symptoms to get tested for COVID-19.
"I know, given winter, that many people have respiratory symptoms at the moment," Dr Spurrier said.
"They might have a mild cold — generally you wouldn't do anything about it, you wouldn't go to your GP, you'd just get over it.
"But now, because of the threat from Victoria, the only way that I can pick if the disease is here is if everybody with respiratory symptoms gets tested."