The number is a drop on yesterday and all 12 are linked to current outbreaks, with 10 of those in quarantine throughout their entire infectious period.
More than 39,000 tests were conducted and 19,000 vaccines administered.
"All Delta and all linked to the NSW incursion," Victoria Health Minister Martin Foley said.
"We had 10 cases in hospital, three in ICU with one on ventilation.
"Overall, we are pleased to see an encouraging trend down in case numbers, and certainly not an increase."
Mr Foley said that the number of people active in the community while infectious is also "trending down".
He said it was however too early to tell whether the lockdown will end as planned on Tuesday.
"(It is) too early to call yet as to what might be the position come Tuesday night," he said.
"As I indicated, 10 of the 12 community cases were in isolation during their entire infectious period, the two cases who were out in the community were only active for less than a day, with only a small number of retail sites being listed for a result."
Of today's 12 new community cases, five are linked to the AAMI Park outbreak.
One is a social contact of a previously identified case that attended the game and four are household contacts of a previously announced case.
Three are linked to Miss Franky's, one is a patron who visited the venue on July 15, and two are household contacts of a staff member.
Two are linked to the Burnley apartment complex.
One is linked to Bacchus Marsh Grammar, a student, and one is a household contact related to one of the generations attached to the Young & Jackson's case.
No cases have been detected that are linked to the Prahran Markets, as was a major concern yesterday.
There are now more than 22,700 close contacts linked to the current outbreak.
Victoria Chief Health Officer Brett Sutton said he is "not taking any chances" with the Delta strain and that's why he declared all of NSW an "extreme red zone from 9pm last night".
"We are not taking any chances with this Delta variant that has come from NSW," he said.
"That's why we have changed the Victorian travel permit system to account for the greater risks posed. I declared NSW in total as an extreme risk zone from 9pm last night, it's backdated 14 days from July 9.
"Victorian residents returning from a red zone who have been in an extreme risk zone in the last 14 days can only enter Victoria with an exemption or another valid permit such as a specified worker permit."
Mr Sutton said sending vaccine doses from Victoria to NSW is "something worth considering".
"It is potentially looking to...try and put the brakes on further transmission, either beyond the area where it (an outbreak) is geographically concentrated or to slow it down over time.
"If that saves thousands of people from infection and many people from dying even if it doesn't have an immediate effect it is something worth considering."
"We need to protect Victorians both from potential incursion, but also all the future risks that will continue to challenge us through to the end of the year.
"Having high vaccination coverage in Victoria is the way to do that, primarily."
Mr Foley stopped short of suggesting Victoria should send vaccine supplies to NSW but said that if there is found to be unallocated doses in the national stockpile, he wouldn't "have any difficulty" in those being prioritised to Greater Sydney.
"The Commonwealth of Australia's greatest need at the moment is clearly the situation in NSW," he said.
"If there is unallocated stock by all means, provided it is not coming at the expense of any state or territory. I'm sure we all support that.
"All of our allocation is allocated.
"I don't think NSW or any other state or territory would expect us to, because they are allocated. That would mean cancelling appointments, that would mean taking arrangements off GPs."
Yesterday, the state recorded 14 new local cases, with three active in the community for about a day while infectious.
Victoria's extended lockdown is due to end at 11.59pm on Tuesday, July 27.
Earlier this week, the Victorian Government declared it needed another seven days to get its outbreaks under control before the state could exit lockdown.
Premier Daniel Andrews said the state could not risk case numbers spiralling out of control like they had in Sydney.
"We need to avoid what is going on in Sydney at the moment," Mr Andrews said.
Victorian Premier calls for 'ring of steel' around Sydney
Mr Andrews called on Prime Minister Scott Morrison on Friday to put a "ring of steel" around Sydney, a move the PM rejected.
Mr Andrews raised the issue at National Cabinet.
"Sydney is on fire with this virus and we need a ring of steel around Sydney," Mr Andrews said.
"There is a national responsibility to do everything possible to contain it where it is now. Not to see it spread."
Mr Morrison rebuffed Mr Andrews' views, insisting it was up to NSW Premier Gladys Berejiklian to manage lockdown measures.
"The only view that matters on this is the view of the New South Wales premier because they are responsible for how they manage the lockdown in New South Wales," he said.
"There is nothing light about the lockdown in Sydney, I can assure you. My family are in it.
"I'm quite certain that people living in Greater Sydney do not feel they are under loose restrictions."
Police, authorised officers and ADF personnel could help man the proposed border around the city to protect the virus from seeping into regional areas and other states, Mr Andrews suggested.
"We did it last year to protect country Victoria and our country, and the same must occur in relation to Sydney.
Sydney streets emptied as new regulations come into force
"There is a national responsibility to put a ring of steel around Sydney."
