Victoria's outbreak of the Delta COVID-19 variant has been linked to a returned traveller who entered hotel quarantine early last month.
Acting Premier James Merlino said authorities had genomically linked the West Melbourne Delta cluster to a Glen Eira man who arrived from Sri Lanka on 8 May.
The same day he tested positive and was moved from the Hotel Ibis to the Holiday Inn "health hotel" on 9 May before being released on 23 May.
Authorities are still unsure how the virus was transmitted from the returned traveller to the infected families.
Acting Police and Emergency Services Minister Danny Pearson said all fellow flight and Skybus passengers had tested negative.
Some 268 COVID-19 Quarantine Victoria staff worked at the Hotel Ibis on 8 and 9 May and 360 staff at the Holiday Inn. All have tested negative.
"I can confirm that so far there is no reported or obvious breach of infection prevention control protocols or anything else that would indicate a transmission has happened inside the hotel," Mr Pearson said.
Mr Merlino said he wanted to reassure Victorians that the revelation would not set back plans to ease restrictions for Melbourne and regional Victoria at 11.59pm on Thursday.
"Our contact tracing team has done exactly what we needed them to do," he said.
"They have found the cases, they have tracked them down and they have isolated them."
Victoria reported two new locally acquired cases of COVID-19 on Tuesday morning.
The two infections were detected in the 24 hours to midnight on Monday, taking the total number of local cases to 85.
An overseas acquired case was also found in hotel quarantine.
Some 22,814 Victorians were tested on Monday and 21,192 received a vaccine dose at state-run sites.
A string of new exposure sites have been added to the list of over 300, including multiple McDonalds, Chemist Warehouses and 7Elevens.
The 18 new "tier two" sites are spread across locations in Yarraville, Maribyrnong, Southbank, Port Melbourne, South Melbourne, Flemington, Strathmore, Coburg North, Mickleham, Campbellfield and Melbourne's CBD.
Anyone who visited the venues at specific times must get a test and self-isolate until they receive a negative result.
Before the emergence of the new exposure sites, Victoria's Chief Health Officer Brett Sutton said Melbourne's lockdown was on track to end at 11.59pm on Thursday.
But he ruled out a return to the relaxed restrictions that were in place before the outbreak
"It is certainly not a snap-back to large gatherings and a full MCG," Professor Sutton said on Monday.
Asked what restrictions would look like come Friday, he said: "It's not something I can speak to now. It's early days still."
Mr Merlino had previously flagged Melbourne would move to a similar set of restrictions to that of regional Victoria, with people unable to travel during the Queen's Birthday long weekend.
A Melbourne CBD construction site remains a key focus of contact tracers as they hunt down virus cases linked to the current Victorian outbreak.
Authorities have confirmed the virus spread from a cleaner who had tested positive to another worker at the ProBuild site at 100 Queen Street in early June.
There are 492 close contacts linked to the site, with more than 400 returning negative tests as of Monday night.
Some 5800 people are still in quarantine, but about 1000 people finished quarantine on Monday after returning day 13 negative tests.
More than 570,000 tests have been administered in Victoria since the outbreak started two weeks ago.
