South Australia has three new cases of locally acquired coronavirus after a worker from a quarantine hotel infected family members.

An 80-year-old woman was diagnosed on Saturday and a woman in her 50s and man in his 60s were diagnosed on Sunday, Chief Public Health Officer Nicola Spurrier told reporters.

“One of those people works in our medi-hotels,” Prof Spurrier said.

“This is where we consider the source to be.”

Contact tracing is underway.