The rate of Victorians testing positive has risen from 4.1 per cent on December 28, when 2738 of 66,683 tests came back positive, to 19.4 per cent on Monday, with 8577 positive results from 44,168 tests.

Portland's testing site at Portland District Health was seeing extremely high demand on Monday morning with bookings filled half-an-hour before the clinic opened, which sent officials scrambling to recruit all available extra staff. Wait times of more than 3.5 hours had been reported at Western District Health Service in Hamilton.

Meanwhile, other testing sites had closed for the holiday period, such as South West Healthcare's Warrnambool and Camperdown clinics.

Active cases as of January 3 in south-west Victoria are:

Rapid antigen tests are also in short supply following the tightening of PCR test requirements to only those with symptoms, household contacts or a positive rapid test.

Many Warrnambool residents took to The Standard's social media to report their struggles in trying to track the kits down and pharmacies posting signs alerting potential customers of their lack of stock.

Victoria has recorded more COVID-19 in the first three days of 2022 than whole of 2020.

One in five cases tested in Victoria is coming back positive, marking a ten-fold increase in the space of a few weeks.

Deakin University chair of epidemiology Professor Catherine Bennett said while the increased rate of positive tests appeared alarming, it was to be expected as testing requirements became more targeted.

Professor Bennett said as the Omicron variant continued to spread and testing queues continued to grow, the daily number of new cases would become less reliable and less important than the number of people in hospital.

"When you look at the hard measures and hospitals are a hard measure, if someone's really unwell, they have to go to hospital and they would be tested, so they're more comparable to compare hospitalisations across states," she said.

"We just do not know how many cases we have out there, what we're worried about is how many people are in hospital and trying to keep transmission low enough to protect that end of it.

"They're the numbers we can look at and the only numbers that are reliable and that we can compare from now going back. The daily case numbers give you some indication in that they're a minimum number, but the true number could be twice that, who knows?"

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