The Department of Health issued an alert late Wednesday asking anyone who visited the Sunbury Square Shopping Centre on February 5 between 3.40pm and 4.30pm to get tested and isolate until they receive a negative result.
They described the move as a “precautionary approach” after a hotel quarantine worker visited multiple stores while infectious with COVID-19.
The advice contrasts with that of other exposure sites, where people who attended must get tested and isolate for 14 days regardless of the result.
Anyone who visited the Sunbury shopping centre outside the timeframe is not considered to be at risk but should monitor for symptoms and get tested if they develop.
It comes as a worker and a returned traveller from the Holiday Inn at Melbourne Airport tested positive for COVID-19 on Wednesday afternoon.
The infections, which will be included in Thursday’s case tally, bring the total number of cases linked to the outbreak to eight.
The outbreak now encompasses three workers, two released guests and a family of three who contracted the virus overseas.
Two banks at Glen Waverley in Melbourne’s southeast have been added to the list of potential exposure sites, which are spread across the city.
It is unclear whether the banks were visited by either the hotel worker, former guest or other previously announced cases.
The outbreak has forced the hotel’s closure until further notice, while plans to increase the state’s weekly cap on international arrivals from 1120 to 1310 from next week have been put on hold.
Authorities suspect a nebuliser, which vaporises medications or liquids into a fine mist, may be to blame for the outbreak.
The medical device was not declared by one of the family members in quarantine, who has an underlying health condition and was taken to intensive care on Tuesday.
COVID-19 Quarantine Victoria Commissioner Emma Cassar said the guest would have been taken to a medi-hotel if they had reported it.
More than 135 hotel staff were stood down and told to get tested and isolate at home for 14 days, while 48 guests were moved to the Pullman Melbourne to quarantine for at least another three days.
Chief Health Officer Brett Sutton said it was possible everyone on that hotel floor had been exposed to the virus through the air and warned more cases would likely be unearthed.
There have been seven cases of COVID-19 transmission across three Victorian quarantine hotels within a week, with three confirmed to be the more infectious UK strain.
Australian Medical Association president Omar Khorshid said the UK strain had “blown open cracks” in hotel quarantine infection controls.