Of the new cases, 17 have been linked and 15 were in isolation while infectious. The other four cases are under investigation.

There are two additional cases acquired interstate.

There have not been any cases confirmed in regional Victoria throughout the sixth lockdown.

There were 45,408 tests returned in the 24 hours up until midnight on Wednesday and 25,418 vaccinations administered.

It marks the second-highest daily vaccine number for the year.

There are 240,000 vaccination appointments available across Victoria over the next four weeks.

There are now 137 active cases in Victoria and 330 exposure sites with 37,000 primary close contacts.

Yesterday 9600 people came forward to get their first dose of AstraZeneca with another 11,600 people booked in for AstraZeneca this week.

248,164 vaccines are booked in for the next month.

COVID-19 testing commander Jeroen Weimar encouraged those eligible for Pfizer or AstraZeneca to book in.

"It's time to get our vaccination journey done," he said on Thursday.

"Over the last six weeks we've seen a growing level of pressure within the New South Wales pressure cooker; we're seeing more cases build up day by."

He said yesterday's mystery cases have been genomically linked to the wider Hobsons Bay cluster.

The two interstate positive cases were two women who flew into Melbourne from Sydney on flight QF471 - carrying 46 people - and were stopped and taken into hotel quarantine.

Yesterday both of them tested positive, showing the high risk of interstate travel, Mr Weimar said.

"This is why we are putting such significant barriers in place."

The others on the flight have gone into quarantine for 14 days.

Over the last month 6000 passengers have been stopped at Melbourne Airport and either put in hotel quarantine or sent back.

The Victorian government announced a rescue package for businesses affected by the extended Melbourne lockdown.

The $367 million package will support more than 100,000 predominantly Melbourne businesses affected by a second week of lockdown.

It will be the third round of funding in as many weeks, with $800 million in support already announced.

Melburnians were told on Wednesday they will spend another week in lockdown, with Premier Daniel Andrews warning Victoria would find itself battling a similar outbreak to NSW were the state to open up now.

"We would see cases akin to what's happening, tragically, in Sydney right now," he said.

The lockdown, the state's sixth, had been due to end on Thursday but will be extended until 11.59pm on August 19.

Restrictions have been lifted in regional Victoria, but those living on the Victoria-NSW border will need a permit to travel between states from Friday evening.

Mr Andrews said there was no option but to extend the lockdown.

"There are too many cases, and too many cases the origins of which are not clear to us, too many unanswered questions, too many mysteries for us to safely come out of lockdown now," he told reporters.

See the exposure sites here.

Latest data shows Warrnambool is leading the way with strong vaccination rates.

The news comes as Warrnambool's vaccine rollout stepped up to another gear, with young people aged between 18 and 39 taking up COVID-19 vaccine at the mass vaccination hub.

We have removed our paywall from our stories about the coronavirus. This is a rapidly changing situation and we aim to make sure our readers are as informed as possible. If you would like to support our journalists you can subscribe here.