COVID-19 appears to have jumped between neighbouring rooms in hotel quarantine in Sydney, after seven cases of people arriving from different countries were revealed to have the same viral sequence.
NSW Health says it was notified that the returned travellers had the same viral sequence on Friday.
The cases may have to be reclassified as locally-acquired cases.
The seven cases came from two family groups who arrived from different countries on different days.
They stayed in adjacent rooms on the 12th floor of the Adina Apartments Hotel at Sydney's Town Hall.
Staff who worked on the floor when the original case is believed to have been infectious - between April 8 and 11 - are now self-isolating.
NSW Health says all security staff who worked on the 12th floor at the time have had at least one vaccination.
The others in quarantine on the 12th floor at the time have all been retested and returned negative results.
NSW vaccinated 4018 people in the 24 hours to 8pm on Friday, bringing the state total to 173,302.
Seven new cases were recorded in hotel quarantine, from 8763 tests.
Australian Associated Press