Deakin University's epidemiology lead Catherine Bennett said Ballarat has always been, and remains, at risk for new active COVID-19 cases but the chance of becoming a hotspot in lockdown remained low, despite a seeming encroachment of the virus from the city's west.

Brimbank (which includes part of Sunshine and Deer Park), Melton and Wyndham (Werribee) have experienced a spike in cases the past week. Parts of Brimbank are already back in stricter lockdowns with Wyndham listed among areas facing a potential tightening with Victoria recording a further 66 coronavirus cases on Friday.

Professor Bennett said the bulk of new COVID-19 cases were still a result of the quarantine hotel leak with cases found in an increase in routine testing for the virus.

She said lockdowns made contact tracing easier and a focus on suppressing suburbs helped to both better contain spread and give health authorities a more complete picture on the outbreak.

"There's always a risk an individual might lead to more cases in a region but one in the wrong place, like a workplace where virus' spread quickly, or a well-connected household group can create a cluster outbreak.

"For the rest of us, restrictions should not be eased until things are under control...We can hope these communities doing it tough are doing the right thing, but we're all in this together and doing it well."

Ballarat would need to chalk up more than 20 COVID-19 cases, with at least five active cases, before it was sent into tighter lockdowns, City of Ballarat has flat-lined on 11 cases since mid-May and has no active cases.

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To go into lockdown, a local government area must have at least twice the infection rate of the state, Victorian authorities said on Tuesday.

More than 10,000 people have refused to be tested in the Victorian government's latest testing blitz in hotspot metropolitan suburbs. Victorian Health Minister Jenny Mikakos said most of those who refused cited a conspiracy or belief the virus would not affect them.

Ballarat Health Services acute operation director Ben Kelly has maintained Ballarat residents should not get complacent. Mr Kelly said, leading into school holidays, social distancing and good hygiene remained the city's greatest defence from the virus. Anyone with even the mildest cold or flu-like symptoms is urged to get the free screening test, by appointment, at the UFS-led clinic in Lucas Community Hub.