The state will enter a seven-day lockdown after 11 new cases were recorded overnight, bringing the cluster of infections to 26.

One of the people infected has been placed on ventilation in an intensive care unit.

The flare-up was sparked by a man who caught coronavirus while in hotel quarantine in Adelaide before travelling on to Melbourne.

Acting Premier James Merlino emphasised the hotel quarantine breach when announcing the statewide lockdown, which begins at midnight.

He also criticised the pace of the vaccine rollout.

“The vaccine rollout has been slower than we had hoped. It’s not where we hoped it would be, it’s not where it should be,” Mr Merlino told reporters in Melbourne on Thursday.

“If more people were vaccinated, we might be facing a very different set of circumstances than we are today, but sadly we are not.”

Federal opposition health spokesman Mark Butler said the Morrison government was to blame for the outbreak.

“This is the 17th outbreak from hotel quarantine in just the last six months. We’re dealing with these outbreaks almost every week or two at the moment,” Butler said.

“Experts advised the prime minister to put in place dedicated fit-for-purpose facilities to take the pressure off hotels that were built for tourism, not medical quarantine.”

Scott Morrison has repeatedly claimed hotel quarantine is 99.99 per cent effective in containing coronavirus.

Butler suspects the prime minister arrived at the figure by dividing the number of people who have gone through quarantine by the number of leaks.

“The problem though is it ignores the fact that every single leak is a massive disaster.”

The federal government has described a Victorian proposal for a purpose-built site as “excellent” but has still not signed off on the project.

Epidemiologist Nancy Baxter cannot understand why there aren’t more purpose-built quarantine facilities like the one at Howard Springs.

“I can’t think of a rationale for not trying to improve quarantine,” she said.

“If it’s the money, how much money is it going to cost to shut down Melbourne for a week?”

There are 29 aged care facilities in Victoria that are yet to receive any vaccines from the federal government.

Aged Care Minister Richard Colbeck defended the delay.

“They were programmed to be done this week or next week, so we’ll get those finalised as quickly as we can.”

Senator Colbeck said he was “very comfortable” with the rollout in aged care, with about 85 per cent of residents taking up the vaccine.

“We offered them vaccination in residential aged care first because they were the most vulnerable … people have made their choices.”

Butler said it was yet another failure of the federal government.

“There’s no shortage of supply – it can only be the system the government has put into place is falling down.”

The Commonwealth has offered Victoria an extra 130,000 doses in a bid to fast-track the vaccination of people in aged care, as well as the broader over-50 population.

States and territories have imposed travel restrictions in response to the Victorian outbreak.