A patient infected with a mutant strain of COVID-19 who was hospitalised in Adelaide is now in a critical condition, health authorities have confirmed.

The man, in his 40s, is one of 12 people in South Australia with COVID-19, all of whom acquired the virus overseas.

SA Health moved the man, who has the South African variant of the virus, from a dedicated quarantine hotel for positive cases to the intensive care unit at the Royal Adelaide Hospital.

SA Health confirmed to NCA NewsWire the man’s condition had been upgraded from serious but stable to critical.

He is the first person in South Australia to be admitted to ICU with coronavirus since May last year.

It comes a day after SA acting chief public health officer Michael Cusack said the man had the South African variant, which contains a mutation which appears to make it more contagious.

“One person was taken from Tom’s Court (medi-hotel) to the Royal Adelaide Hospital this morning because they were unwell and are currently being assessed there,” Dr Cusack said on Saturday.

“This is a male in his 40s we believe has the South African variant.

“Clearly if someone is deemed unwell enough that they have to go to hospital, we have concerns for their welfare, but obviously they are in the right place.”

Dr Cusack said the patient had been suffering shortness of breath.

“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 the Royal Adelaide,” he said.

South Australia recorded just one COVID-19 case on Sunday which was a child who had returned from overseas and is in isolation.

The state also administered 145 vaccinations for COVID-19 on Saturday, bringing the total to 28,759.