Eighteen of the state's 80 new infections on Thursday are linked to the outbreak in the town, about 180 kilometres north of Melbourne. None were isolating throughout their infectious period.

It brings the total number of cases in Shepparton to 67, though Goulburn Valley Health chief executive Matt Sharp confirmed at least another five or six cases had emerged by Thursday afternoon.

Up to 20,000 residents in the region, which has a population of 65,000, are believed to be self-isolating.

Food distributors, supermarkets and pharmacies are among businesses forced to reduce operating hours due to staff shortages.

Mr Sharp said the health department was working to downgrade local tier-one exposure sites, particularly those involving schools, to release close contacts from isolation quicker.

Earlier on Thursday, Premier Daniel Andrews announced the state's deputy emergency management commissioner Deb Abbott, as well as other senior departmental officials, had been sent to Shepparton to co-ordinate relief.

"It is no different to a bushfire or flood. The emergency management architecture will be in place but it will be in the main very, very simple things - taking food to people's doorstep, getting scripts filled," Mr Andrews told reporters.

"The focus is on getting everybody in Shepparton things they need when they need them."

About 70 ADF personnel will support testing and door-to-door checks over the next one-to-two weeks, with up to 25 members trained and deployed on Thursday afternoon.

Independent Shepparton MP Suzanna Sheed said she spoke with Mr Andrews on Wednesday night and secured urgent support, including medical staff to replace some of the more than 500 furloughed GV Health staff.

Opposition Leader Michael O'Brien said the government had taken too long to send help to suffering Shepparton residents.

Of the 80 new cases in Victoria, 67 are linked to known outbreaks, while the source of 13 infections remains under investigation. Forty-one cases were infectious in the community.

Mr Andrews said several new cases had experienced COVID-19 symptoms for a week or more before getting tested.

"When you register a symptom, you cannot wait seven or eight days, as regrettably some of the positive cases did wait a long time before going to get tested," he said.

"(It) meant they were in a community, out there unknowingly infecting other people and often the people they love the most."

Mr Andrews urged Victorians to abide by stay-at-home orders, as there were "not many more levers" left to rein in rising case numbers.

"The longer people break the rules or make a judgment that the rules don't apply to them, the longer these rules will be on," he said.

"The more cases we have, the more cases that will be in hospital. That's not being alarmist, it's just being factual."

There are 600 active COVID-19 cases in Victoria, including 36 people in hospital, with 11 in intensive care and eight on ventilators.

Meanwhile, about 200,000 Victorians booked in to receive a COVID-19 vaccine on Wednesday, after eligibility opened up to those aged between 16 and 39.

On a typical day some 30,000 vaccine bookings are made.

Australian Associated Press