Premier Daniel Andrews said on Saturday the public housing crackdown would effect 3000 people and would required an unprecendented level of help from police.

"There will be no one allowed in...and no one allowed out," he said.

Residents in the Flemington and Kensington public housing units who are some of the city's most vulnerable will receive food deliveries and medical, drug and alcohol support.

There are 509 active cases with 25 people in hospital and three in intensive care.

The extra Melbourne postcodes to be locked down from 11:59pm tonight are 3031 and 3051.

As of Friday, Ballarat remained without an active case. Saturday's location data has not yet been released.

Read Mr Andrews statement in full below.

Today's numbers represent the second biggest increase in confirmed case since this began - and the biggest jump since 28 March.

As these figures show, we are still on a knife's edge.

Rather than spread across the state, we know many of these cases are located in specific communities.

That means the need for targeted, swift action is stronger than ever before.

In recent days, 23 cases across more than 12 households have been identified in the Flemington and North Melbourne public housing estates.

This represents a challenge we've not yet encountered. This is not like an outbreak spread across multiple homes or multiple suburbs.

The close confines and the shared community spaces within these large apartment blocks means this virus can spread like wildfire.

And just like fire, we need to put a perimeter around it to stop it from spreading.

It's why, effective immediately, these estates - encompassing nine sites - will be closed and contained.

Residents will be required to stay inside their homes.

Just as we've done with similar outbreaks in closely confined settings like aged care, the only people coming in and out will be those providing essential services.

This will be in place for at least the next five days, ensuring we can test every single resident.

The lifting of this restriction will be determined by our success in testing and tracking this virus.

Operation Benessere will be supported by onsite police and PSOs, ensuring safety, compliance and security.

Residents will be supported with onsite clinical care, as well as food delivery and care packages.

I know this is big. And I know this is unprecedented. But as always with this thing, an unprecedented challenge requires unprecedented action.

On the advice of our health experts, the number of "hot zone" postcodes will also be expanded to include 3031 and 3051. This will be effective from 11:59pm tonight.

For residents in these postcodes, the message is clear: stay at home.

There's only four reasons to be out. Again, shopping for food and essential items. Care and caregiving. Exercise.

Work and study - if you can't do it from home.

These postcodes are experiencing elevated community transmission - and the only way to combat that is with stronger restrictions.

But it's not just enough to impose them.

We need people to abide by them. To follow the rules. To listen to the advice.

To think not only about themselves but their families and friends and communities.

This virus is dangerous. It's indiscriminate. And it has the potential to undo everything that's been achieved.

I understand people are tired. They're frustrated too.

But just as we drove down this virus before, we must do it again.

We need Victorians - your collective commitment and courage.

Because we all have a part to play.

And it's up to all of us to make this work.