As 73 new Covid-19 infections were reported in the state, Victorian Premier Daniel Andrews has warned state-wide lockdown is an option if outbreaks continue.
From 11:59pm on Wednesday, about 311,000 residents in 10 postcodes will be restricted from leaving the house except for essential purposes.
Andrews said announcing the move last night had been a "difficult call", but he had been given public health advice to shut down the hotspot suburbs immediately or face "shutting down all postcodes later".
Stage three restrictions would remain in place in those areas until at least 29 July.
Of the new infections recorded overnight, three were detected in hotel quarantine and nine were linked to known outbreaks, 19 were detected through routine testing and 42 cases remained under investigation.
"If we don't get control of this really quickly we will end up with ... a whole state shutdown," Andrews said.
"This is not over. This is so wildly infectious that even minor breaches of the rules can lead to this random movement of the virus around the community."
Victoria postcodes under stay-at-home orders from Thursday:
- 3012: Brooklyn, Kingsville, Maidstone, Tottenham, West Footscray
- 3021: Albanvale, Kealba, Kings Park, St Albans
- 3032: Ascot Vale, Highpoint City, Maribyrnong, Travancore
- 3038: Keilor Downs, Keilor Lodge, Taylors Lakes, Watergardens
- 3042: Airport West, Keilor Park, Niddrie
- 3046: Glenroy, Hadfield, Oak Park
- 3047: Broadmeadows, Dallas, Jacana
- 3055: Brunswick South, Brunswick West, Moonee Vale, Moreland West
- 3060: Fawkner
- 3064: Craigieburn, Donnybrook, Mickleham, Roxburgh Park and Kalkallo
New testing sites set up in focus suburbs
More than 113,000 people have been tested as part of the blitz since it began last week, including more than 20,000 on Tuesday.
"That's such a powerful contribution to the fight against this virus," Andrews said.
Workers have already knocked on 54,000 doors in high-risk suburbs and will be fanning out across suburbs including Maidstone, Broadmeadows, Albanvale and in Brunswick West later this week.
Andrews and Health Minister Jenny Mikakos announced 12 new testing sites were being set up in suburbs where community transmission was a concern.
Andrews said residents in postcodes not under lockdown still had a part to play in slowing the spread of the virus, warning people must not go out if they felt sick.
He said a "booze bus-type arrangement on main thoroughfares in and out of the areas" would be set up to enforce the restrictions.
"There will be random checks about why people are out of their house and if they have a valid reason," he said.
"I hope we don't have to issue any fines but unless you enforce these rules they won't be followed."
Andrews said if people did not follow the rules and cases continued to rise he would "be locking down all suburbs".
He said in order for the 10 postcodes to reopen, health authorities needed to see daily cases driven down.
"The message is really clear if you want to see these lockdowns eased ... follow the rules, use common sense, don't pretend it's over," he said.
"If someone comes to your doorstep and offers you a test, the right answer is yes.
"If this continues to get away from us we will all be in lockdown."
Mandatory testing a 'last resort'
Acting chief medical officer Paul Kelly called the Victorian measures "strong and appropriate" and supported the Premier's warning that further lockdowns could be needed.
"Very clearly they will be expanded if necessary and, importantly, they will be enforced," Prof Kelly told ABC's RN Breakfast.
"We are looking very closely. That's always a possibility.
"We know where the cases are and we have a large testing program. We will know if it's working."
More than 900 people in Broadmeadows and Keilor Downs alone have refused to have a test and there have been questions about whether they should be mandatory.
Professor Kelly said that should be a last resort.
"All of the state and territory chief health officers have powers under their public health acts that can make testing and other mechanisms mandatory," he said.
"But it's a last resort. I think explaining and getting cooperation is the first way."
"I think 100,000 have said yes [to testing] so let's concentrate on the positive," he said.
Andrews also rejected making testing mandatory.
He said it would require a police officer having to go door-to-door with health officials in the lockdown suburbs, which would create practical problems.
"We urge people to get tested," he said.
Professor Kelly said wearing a mask in the affected areas could be part of the solution.
"If people are in that setting and cannot avoid large groups of people, masks may be part of the solution, but it's not the only solution," he said.