Health Minister Martin Foley on Monday confirmed four of the state's 11 new cases were linked to the state's outbreak of the Delta variant, also known as B.1.617.2, which began in the suburb of West Melbourne.
The cases are three children and an adult. It brings the total number of cases in the outbreak to 14.
Four of the new cases are linked to the city's outbreak of the Kappa or B.1.617.1 variant, which began in the City of Whittlesea and has spread to several locations across Melbourne, including Port Melbourne.
The outbreak now totals 33 active cases in Whittlesea and 31 in Port Melbourne.
The remaining three cases are linked to an outbreak of the Kappa variant at the Arcare Maidstone aged care facility in Melbourne's northwest, two of which were announced on Sunday.
The additional case is an aged care worker.
State testing commander Jeroen Weimar said more than 5800 people were quarantining after coming into contact with a positive case, while there were 350 exposure sites across Victoria.
About 1000 people had ended quarantine following a negative day 13 test, he said.
Authorities still don't know how the Delta variant has spread in Melbourne.
Infectious diseases expert Sharon Lewin suspects the variant could have leaked from a hotel quarantine or from a returned traveller who was provided with an exemption to isolate at home.
"There are exemptions for diplomats and other people ... but those are actually really quite rare," she told 3AW radio.
"That is another source that the authorities are going to be investigating."
Professor Lewin and her team continue to comb through genomic sequencing data from across the country for answers.
It is unclear if the new cases will dent Melbourne's hope of emerging from lockdown on Friday but Professor Lewin remains optimistic.
"It really depends on the data that we're going to hear about today about the origin of these nine cases. But so far so good," she said.
Victoria's Deputy Chief Health Officer Allen Cheng on Sunday said he expected restrictions would be eased as planned.
"Given five per cent of Victorians have been tested in the last seven days, if there was a big outbreak going on I would expect to have picked it up," he said.
"That risk does fall over time but we are still concerned about that and that is where all our efforts are going."
Professor Cheng said there was no "magic number" of people getting the jab to avoid future lockdowns, with only two to three per cent of Victorians fully vaccinated.
"Once you get up to much higher coverage rates, then it makes a whole lot of things easier," he said.