Acting Premier James Merlino has announced a new mask mandate, with Victorians aged eight and over required to wear masks indoors from 11.59pm tonight.

The announcement came as Victoria recorded a jump in cases, with 2005 new cases throughout the state.

Face masks will also be required at any events with over 30,000 people, although patrons can remove their masks at such events when seated outdoors.

Mr Merlino said hospitality venues had been issued a strong recommendation to only offer seated service, and to remove indoor dancefloors in an effort to avoid patrons moving around crowded venues.

"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," Mr Merlino said.

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He also announced $31.6 million to support the Commonwealth government's vaccine booster rollout.

"This investment will mean that if the Commonwealth can meet the doses they have projected, up to 900,000 doses can be delivered every week in Victoria," he said.

Health Minister Martin Foley announced 28 new vaccination sites as well as expanded opening hours for currently operating centres.

On Thursday vaccination centres across Melbourne began accepting walk-in boosters for people with a four-month interval since their second vaccine shot, rather than the five months recommended by ATAGI.

The Victorian Department of Health said the routine interval for booster shots remained at five months, but vaccination centres would not turn away people who were just under that interval.

A spokesperson for South West Healthcare said anyone who had their second dose at least four months ago could receive a booster at the Warrnambool Vaccination Centre, but the centre is currently closed and will not be reopening until January 7.

Booster doses are available through local GPs and pharmacies, but only with a five month interval.

He encouraged parents of children aged 5-11 to get them vaccinated when that program begins on January 10.

"Those 570,000 kids in that age bracket are locked in for their support for their vaccines over January," he said.

Chief Health Officer Brett Sutton said the Victorian vaccination program was already ramping back up as increasing numbers of people received their booster doses.

"We are reporting over 16,000 doses delivered through state run centres yesterday. That is double what it was a week ago, and a week ago is double what it was the week before that, so it is really ramping up which is fantastic," he said.

He said Victoria passed the milestone of 5,000,000 COVID-19 vaccine doses administered on Thursday.

Dr Sutton defended the decision to impose a new mask mandate while Prime Minister Scott Morrison refused to do so.

He said the evidence showed a significant difference in public compliance between something being "highly recommended" and being mandated.

"We usually get about 50 per cent levels of cooperation or compliance with a strong recommendation. It goes to 95 - 99 per cent with a mandate.

"Why would you introduce a half measure when you need the full measure to be in place?"

Dr Sutton also explained the government's campaign to reduce the booster interval from five months to four.

"We have got an immediate challenge (from the Omicron variant). You have got thousands upon thousands of people who have had to get doses who are not yet boosted who we know are still at significant risk if they have got preexisting conditions," he said.

He warned that while the emerging data was pointing toward Omicron causing less severe illness than the Delta variant, it was also much more infectious, meaning the strain on public healthcare systems was still a major concern.

"New South Wales has 15 times the number they had just a couple of weeks ago, so one-fifth as severe but 15 times as many cases is going to be a challenge to a health system," he said.

On Thursday afternoon NSW Dominic Perrotet also decided to reintroduce masks in indoor settings.

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