Victoria has confirmed another massive spike in virus cases, with 216 new infections recorded overnight.
Victorian Premier Daniel Andrews also revealed a man in his 90s died in hospital overnight from the virus.
He warned residents that if the virus isn't brought under control then "it will spell tragedy for many more Victorian families".
Yesterday the state recorded 288 new Covid-19 cases, the highest spike since the pandemic began.
Australia has recorded a total 9171 cases of Covid-19: 3278 in New South Wales, 3379 in Victoria, 1007 in Queensland, 443 in South Australia, 630 in Western Australia, 228 in Tasmania, 113 in the Australian Capital Territory and 30 in the Northern Territory.
Virus in 'every part' of Melbourne
Andrews has warned Melbourne residents the virus is in "every part" of the city.
"We've seeing significant numbers out of the northern western suburbs, but it's in other parts of Melbourne," he said.
"I wouldn't want anyone in Melbourne to think this isn't relevant to you. It is relevant to your family, your street, your community and all of us. We've all got a part to play.
"It is in every part of Melbourne. Some at very low levels but it won't be at low levels for long if people don't follow the rules."
From Monday, Year 11 and 12 students, along with specialist schools and Year 10 students doing VCE subjects, will return to classrooms.
For all other students, school holidays have been extended by a week.
Andrews assured parents and carers that temperature checking would be in place for those children going back to school next week.
"I want to reassure all parents with students in those year levels and settings there will be temperature checking, there will be all sorts of different processes and protocols, strengthening, building on the great work that our schools did at the back end of the last term," Andrews said.
"I know school communities take this very, very seriously. There will be options for more distance, because we have less than a full school. We have only a small number in the overall number of students attending each school.
"The other point on specialist schools, we've listened to parents of children with those highest needs and it's not practical for them to be schooled at home, it's really challenging.
"So those schools are open for that reason as well. Lower risk, and really the alternative is not an appropriate one."
Andrews has sent out a stark message to rule-breakers, saying police won't be issuing any warnings before handing out fines to people doing the wrong thing.
"There's no need for anyone to get fined. These rules are really clear. If you do the right thing, you won't be at any risk of getting a fine, but if people do the wrong thing, then this is so serious," he said.
"The stakes are so high. The police will not issue warnings. The commissioner made it clear. That's his call. I support the call he made. These rules are not new."
It comes after 16 people were fined for breaking lockdown rules to attend a birthday party.
Andrews said he didn't think it was too much to ask of Victorians to only go out for the four reasons allowed under stage three restrictions.
"We are not asking you to enjoy it, no-one will be enjoying it. It's what has to be done and police are out there in force, well supported by the Australian Defence at checkpoints and other important functions that Victoria Police have stood up to have that hard border," he said.
"I would thank every Victorian doing the right thing. That's the vast majority. That's a deeply impressive thing.
"There will always be a small number who don't do the right thing. Not only is it wrong, it's not very smart. Victoria Police will catch you."
Andrews said if people made "selfish choices" and flout the rules, the lockdown would be extended.
More than 100 different outbreaks in Victoria
Victoria's chief health officer Brett Sutton has revealed the state now has "over 100 cumulative outbreaks" of Covid-19.
He said there were multiple cases emerging from staff members in aged-care facilities.
"That's the workforce that we have to be really mindful of. The response in each and every aged-care facility is to go into lockdown for those residents and all staff to be tested and for them to go into quarantine period of 14 days and to have that testing before that quarantine is lifted for all residents and staff members," Sutton said.
"But it flags the dangers in aged-care facilities. Victoria had more outbreaks there than any jurisdiction, but we haven't had an aged-care facility that has had a substantial outbreak.
"I think that's in large part because we had the early robust response in terms of testing everyone and going into lockdown."
Test result wait times up to three days
Victorians who are tested for Covid-19 can expect to wait between two to three days for the results.
Health Minister Jenny Mikakos said that was because of the "huge volume" of testing occurring across the state.
"Our capacity and our pathology labs has increased. We have a capacity in Victoria to do about, to process about 25,000 tests per day," she said.
"We also are utilising the additional capacity of interstate labs as well. I took the opportunity before to thank our interstate labs for their assistance. So the time frame is still good.
Mikakos stressed that anyone who is tested has to self-isolate while they wait for the results.
"The risk is if they are positive and go to work and move around they could infect others," she said.
"That is why we had the hardship payment and other supports available to people to make sure that there is no disincentive to people pursuing a test and staying home and isolating if they do test as positive to ensure that they don't lose a couple of weeks' pay and they have that hardship payment of $1500 available from the Victorian Government if they can't access their own sick leave or other workplace entitlements."
Effect of lockdown known within the next few days
Chief health officer Brett Sutton said the impact of the lockdown on the spread of the virus should start to become clear within the next three to five days.
"With respect to stage three restrictions across metro Melbourne and Mitchell Shire, it's in the next three to five days that it should be having an effect," he said.
"There are challenges, though. Those restrictions restrictions limit substantially the number of interactions in home, socially, outside, but there are people who need to go to work and when you have a significant pressure of infection that we have with numbers now, we know there will be transmission because of the work people have to do and so we can't be guaranteed that will turn around in three to five days.
Sutton said just having people stay home would not be enough to slow the spread.
"We need to work with the masks, the workplaces, make sure people are doing the right things in terms of excluding themselves unwell and getting tested as part of that as well," he said.