Police and health authorities are investigating how a doctor without registration worked at a regional South Australian emergency department for six days.
The overseas-trained doctor allegedly saw at least 15 patients at Port Augusta Hospital between April 24 and Tuesday this week before being removed.
SA Health said it's not aware of any adverse patient outcomes, but is contacting them to discuss their care needs.
It said the supervising locum doctor has also been stood down and it's launched an investigation, while SA Police and the medical regulator are also examining the case.
"On behalf of our service, I apologise to all those patients who had contact with this unregistered doctor. This incident should not have occurred and I am deeply sorry," Flinders and Upper North Local Health Network chief executive Craig Packard said.
"We have informed SA Police and the Australian Health Practitioner Regulation Authority (AHPRA) and will also conduct a full and thorough review into how this incident occurred."
SA Health said the doctor had been offered provisional registration by the medical board on May 2.
It said he was also offered a place as an intern and had been undertaking limited education sessions in Whyalla.
SA Health CEO Robyn Lawrence said the doctor had access to the site when he wasn't supposed to, and she couldn't say how he was given that access.
"It is completely unacceptable that an unregistered doctor could be in an environment where they have access to patients, without providing their credentials or registration," Dr Lawrence said.
"That is why I have commissioned a full independent investigation into how and why this occurred to make sure it never happens again."
Health Minister Chris Picton said the incident was "completely unacceptable" and never should have happened.
"To the patients of Port Augusta I assure you that this government is taking this matter incredibly seriously, and acting quickly to do everything we can to prevent such an occurrence happening again," he said.
AHPRA's website states that in Australia, the titles of registered health practitioners are protected by law so that patients can assume they are appropriately trained and qualified.