A young girl who travelled from Victoria to visit relatives in Adelaide has tested positive for COVID-19, becoming the state's first locally-detected case after the opening of borders to all states and territories.
The girl came into SA by road with her mother and a sibling and was informed during the trip she was a close contact of a case in her home state.
The family then got tested at Tailem Bend, east of Adelaide, before continuing on to visit relatives.
With confirmation of the girl's infection on Wednesday, Chief Public Health Officer Nicola Spurrier said the family had decided to return to their home in Nhill to quarantine.
The girl's grandparents have been vaccinated and will quarantine at home for seven days.
Professor Spurrier said no other exposure sites had been identified and the risk to the wider community was low.
"The real message here is we are going to have cases in our state," she said.
"This should be a wake-up call for anybody who is not vaccinated. There is going to be COVID in our community."
An old COVID-19 infection was also detected in another traveller from Victoria but was not considered an issue and will not be added to the state's tally of coronavirus cases.
"They're not infectious so they're no risk to the community," Professor Spurrier said.
"In fact, they won't become an active case for us in our state because they've already been counted as a case in Victoria."
Premier Steven Marshall said precautions with remaining travel restrictions would make sure officials could "get hold" of any early virus cases as quickly as possible.
"That means we can push any significant numbers down the track for the next couple of weeks, couple of months," the premier said.
"We know that every day that goes past we get more South Australians vaccinated and that reduces our risk."
Under SA's new travel rules, anyone coming into the state must be double vaccinated and use a new online border entry process known as EntryCheck SA, which assesses an individual's vaccination status, departure location and COVID-19 risk.
Based on the information provided, travellers may also be prompted to use a new HealthCheck SA app, which will help them monitor daily symptoms and guide them through any testing and quarantine requirements.
In most cases, travellers are required to have a COVID-19 test within 72 hours of departure.
Unvaccinated travellers will be required to seek a special exemption with applications to be assessed on a case-by-case basis.
So far more than 60,000 people have registered to come into SA in the coming days and weeks.