Victorians young and old must don masks inside this holiday season under a reinstated mandate to curtail the spread of the Omicron variant.

Two days out from Christmas and as the state recorded 2005 new coronavirus cases and 10 deaths, Acting Premier James Merlino ordered masks for those aged eight and up in hospitality, entertainment and office settings from 11.59pm on Thursday.

Masks will also be required at all major events with more than 30,000 patrons, including the Boxing Day Test at the MCG, but can be removed while seated outdoors.

They do not need to be worn in households.

Mr Merlino described the measures, which will remain until at least January 12, as modest.

"This is a sensible response which will allow businesses to stay open, bars and restaurants to continue to stay open and major events to go ahead," he told reporters.

Federal health officials "highly recommended" wearing masks indoors and in crowded settings at Wednesday's national cabinet meeting, but only states and territories can mandate them.

Before the Omicron variant emerged Victorian planned to relax mask requirements, but last week kept them in retail settings, for hospitality workers and on public transport.

Chief Health Officer Brett Sutton said uncertainty surrounding the new strain lingered, but early evidence suggests it could be a fifth as virulent compared to Delta and far more infectious.

"New South Wales has 15 times the (case) number they had just a couple of weeks ago," he said.

"One-fifth as severe but 15 times as many cases is going to be a challenge to a health system. So we need to do everything we can."

Professor Sutton argued the mask mandate was needed to achieve greater compliance, saying about 50 per cent of people follow a "strong recommendation" compared to up to 99 per cent for an explicit order.

Victorians are also recommended to work from home over the festive season and hospitality venues asked to consider seated service-only.

A lockdown is not being considered because of Victoria's high vaccination rate.

While Victoria and other jurisdictions await Australian Technical Advisory Group on Immunisation advice on reducing the third dose interval, the state government has pledged an extra $31 million to hasten the booster rollout.

Twenty-eight more pop-up vaccination sites will open in the coming weeks and operating hours of the state's 50 fixed sites will extend to 12 hours a day, seven days a week.

Prof Sutton stressed the urgency of the dose interval being shortened from five months, despite his former deputy and ATAGI co-chair Allen Cheng last week saying an early booster could provide less protection and interfere with later variant vaccines.

"We can't just think about how things might look in July of next year," he said.

"We need to think about what the immediate challenge is for those individuals who are not sufficiently protected until they've got that booster."

Thursday's case number is the state's highest since October 22.

Another 10 Omicron cases have been identified, taking Victoria's total to 71.

VICTORIA'S LATEST COVID-19 FIGURES:

* Active cases: 14,801

* Hospital cases: 398

* Active cases in ICU: 72 active cases in ICU

* Cleared cases in ICU: 40

* Cases on a ventilator: 39

* Vaccine doses administered at state-run sites: 16,758

* Tests processed: 85,112