The case, detected in the country’s largest city Sydney, comes despite a ban on non-citizens entering the country and restrictions on flights from southern Africa, where the variant was first detected.
Australia has detected nine other Omicron cases, but all were detected incoming travelers.
The latest case raises the possibility that Omicron may already be spreading more widely in the community. However, the student’s Regents Park Christian School in the west of Sydney has been closed and the family is said to be in quarantine.
Authorities have expressed confidence that with 87 percent of people over 16 years old vaccinated, the country is well placed to deal with the new variant.