The source of the delta variant found in Melbourne on Friday remains a “mystery”, says CHO Paul Kelly.

While authorities are confident it came from someone entering the country from overseas, the new case has not been genomically linked to any other positive cases, and has “no definite link to any particular breach”.

Mr Kelly confirmed that diplomat arrivals, who have been able to quarantine in their own homes in the ACT, have been thoroughly checked as a possible source, and there have been no positive cases.