Acting Premier James Merlino has confirmed another six cases of COVID-19 have been detected this morning, on top of the five recorded overnight.

Mr Merlino said the situation was very serious and cases had been detected in aged care.

"This is not over and we need to keep going," he said.

"I want to be very clear with everyone, this outbreak may well get worse before it gets better."

When asked about lockdown lifting on Thursday as planned, Chief Health Officer Brett Sutton said it was a day-by-day prospect.

"We're neck-and-neck with this virus and it's a beast," he said.

"We need to prepare for anything."

Mr Sutton said the numbers of close contacts was huge.

There are no positive cases in regional Victoria, though there are potential exposure sites.

When asked if a ring of steel would be established around Melbourne to allow restrictions to ease in regional Victoria Mr Sutton said nothing had been decided.

He said there were still a number of close contacts in regional areas.

Mr Sutton said Victoria was ready and willing to assist the Commonwealth government with aged care vaccinations.

Health Minister Martin Foley said a number of the new cases relate to private aged care facilities, with a resident in her 90s testing positive.

One private aged care staff member worked across two Commonwealth run facilities.

He said more than 50 Victorians are currently living with the virus, and many more secondary and primary contacts.

"The fact this outbreak has crept into residential aged care is obviously of great concern," he said.

PREVIOUSLY:

VICTORIA'S list of exposure sites has soared past 270 as the state recorded five new locally-acquired cases of COVID-19 overnight.

An aged care home in Melbourne's north-west is in lockdown after a COVID-positive worker became the state's first "mystery case" of the outbreak.

The Altona woman worked at Arcare Maidstone on Wednesday and Thursday and might have been infectious at the time.

She sought testing as soon as she fell ill on Friday and was among five new locally-acquired cases reported in Victoria on Sunday.

IN OTHER NEWS:

The aged care home has been placed into lockdown and residents are self-isolating, with authorities unsure how the worker picked up the virus.

The woman, a healthcare provider in contact with aged care residents, was vaccinated on May 12.

Authorities administered more than 16,700 vaccinations on Sunday with another 43,874 people who got tested for the virus.

There are now 54 active cases across Victoria.

Meanwhile on Sunday, Victorian Treasurer Tim Pallas announced a $250 million support package to help impacted businesses through the lockdown, something Bendigo businesses welcomed.

A full list of COVID-19 exposure sites is available here.

- with AAP