Two new cases linked to the Holiday Inn at Melbourne Airport were unearthed on Tuesday, including a food and beverage worker and an already released returned traveller.

It brings the total number of cases associated with the cluster to three, with an authorised officer at the hotel testing positive on Sunday.

Chief Health Officer Brett Sutton said the cases are likely linked to transmission on a floor with known COVID-positive guests.

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That includes a family of three, one of whom has been transferred to intensive care.

Mr Sutton indicated the infected workers and former guest appeared to have picked up the virus from the family despite having no close contact as he defended the state's quarantine system.

"Cases can happen anywhere, at any time, and they can happen without a breach of protocol or any particular errors being made," he told reporters on Tuesday afternoon.

"We are talking about an incredibly infectious virus. We have known that airborne transmission is possible.

"The extent to which it occurs and how well you can reduce that risk ... is a matter of ongoing review."

He said health officials needed to continue to investigate every intervention possible to better protect hotel quarantine workers and guests.

"All I can say is bring on the vaccine," he said.

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Earlier, Premier Daniel Andrews said the state had no choice but to "make the best of what we have" in the face of mounting program criticism.

"There's no federal facilities that are going to pop up anytime soon," he told reporters.

At the Holiday Inn, guest arrangements on the affected floor have been pared back and Mr Sutton said authorities could close the hotel if the risk is found to extend beyond it.

Returned travellers from the same floor as the woman who left quarantine on Sunday must now go into isolation for another 14 days. Staff who worked on it will follow suit.

Health authorities overnight issued a notice of several new exposure sites including Sunny Life Massage, Bakers Delight, Aldente Deli, Sushi Sushi and Asian Star - all in Sunbury Square Shopping Centre in Sunbury - as well as Cellarbrations and PJ's Pet Warehouse also in Sunbury.

AAP

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