Doctors are currently working to save the life of a man in the intensive care unit with the highly infectious South African variant of coronavirus.
South Australia Health confirmed the man in his 40s, who on Saturday was moved from a quarantine hotel to hospital, had been shifted to the intensive care unit at Royal Adelaide Hospital.
An alert on Sunday revealed he was fighting for life in a critical condition.
"If someone's deemed unwell enough that they have to go to hospital, we have concerns for their welfare but obviously they are in the right place," SA's Acting Chief Public Health Officer Michael Cusack told reporters on Saturday.
Emergency department workers on Saturday were determining the severity of the man's symptoms, which Mr Cusack believed to include breathlessness.
"Whether they're sufficiently short of breath or their lungs are sufficiently impaired that they will need to remain in hospital is still to be determined by the emergency department at Royal Adelaide," he said.
He is one of a dozen people to have acquired the virus overseas before arriving in South Australia.
The state's one new case on Sunday was that of a female child who had been staying in a medi-hotel since returning from overseas on a recent flight.
SA Health said on Sunday it was believed the case was an old infection that had not been previously been diagnosed or counted.
Meanwhile, a man aged 44 in Melbourne suffered a rare blood clotting disorder after receiving the AstraZeneca Covid-19 vaccine. The incident will not however affect the vaccine rollout in Australia.
In Queensland, health chief Dr Jeannette Young said on Saturday Papua New Guinea's soaring Covid-19 infection rate was "an enormous concern" as health officials raced to vaccinate vulnerable communities in the state's far north.
She added "severely unwell" patients from PNG were being transferred for treatment in Queensland hospitals.
Do you have a story tip? Email: firstname.lastname@example.org