A woman in her 20s who recently moved from Victoria to South Australia has tested positive for coronavirus but is not considered a risk to the wider SA community.
The woman was given an exemption to come to Adelaide at the weekend to start a new job and is now in hotel quarantine.
She travelled to SA with three family members who are in home isolation along with another family member who already lived in Adelaide.
"We're very pleased there has been no exposure to any South Australians at all," Chief Public Health Officer Nicola Spurrier said on Tuesday.
"Our system has worked and the mandatory testing for anybody coming from Victoria did pick up that this woman was COVID positive."
The woman's case takes the total diagnosed in SA since the start of the pandemic to 448 with only three of those considered active.
It came as the state prepared to introduce even tougher border restrictions with Victoria, with Premier Steven Marshall promising all resources necessary to keep the border secure.
The changes from midnight on Tuesday will prevent any South Australians from returning home and will also tighten exemptions to essential workers.
People living in close border communities will be limited to just 40 kilometres each side of the border, further restricting travel between the two states.
Mr Marshall said while there was a reduction in coronavirus infections reported in Victoria on Tuesday, SA remained on high alert.
He said police would have all the resources necessary to keep the border secure, mindful some people would still try to cross despite the threat of heavy fines and possible jail terms.
"We'll continue to keep that border as tight as we can," the premier said.
"We appreciate this is very difficult for families who are going to become dislocated but our primary responsibility is on the health, safety and welfare of our citizens."
As well as tighter restrictions for Victorians, South Australia's transition committee has maintained the current rules for people arriving from NSW and the ACT who are still required to quarantine for 14 days.
Mr Marshall said a number of clusters of COVID-19 infections in and around Sydney, including those emerging from funerals, remained a concern for SA authorities.
"The other clusters are under control but there is no change to our arrangements with NSW or the ACT," he said.