Victoria has posted its worst day of community transmission of COVID-19 yet as cases again spike to worrying levels in the state.

Victorian health authorities confirmed 73 new coronavirus cases on Wednesday, marking more than two weeks of double-digit increases.

The numbers mean the state has 301 confirmed cases of coronavirus acquired through unknown transmission – a rise of 20 from Tuesday.

It came as authorities again pinned the blame for the escalating spread on problems with the state’s hotel quarantine system.

“There’s been a failure of that quarantine, clearly, in Victoria,” acting chief medical officer Paul Kelly said on Wednesday.

“We absolutely need to learn the lessons of that. It does demonstrate how infectious this virus is and how easily it can spread when infection control is not adequate.”

He said the outbreak was being treated as a national issue.

“Whilst this is an issue in Victoria at the moment, this is very much a national response,” he said.

Earlier, Premier Daniel Andrews warned the whole state faced the threat of renewed lockdowns unless the virus can be brought under control.

Since Monday alone, Victoria has added 212 confirmed COVID-19 infections – the vast majority picked up in a community testing blitz. Its numbers far exceed those of any other Australian state.

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The latest dire figures came just hours before the 10 Melbourne postcodes with the highest number of COVID-19 infections return to strict stage-three lockdowns.

From 11.59pm on Wednesday until at least July 29, more than 300,000 residents will be allowed to leave their homes only for work, study, essential shopping, exercise or to receive or give care. Mr Andrews defended the drastic move, which has sparked community anger.

“It’s not as if I sat down with a map and drew these boundaries. They have been drawn by our public health experts based on data,” he said.

“The alternative is to say, let’s take the broadest brush we can and lock down the entire north or west of the city, or even further still, let’s lock down the entirety of metropolitan Melbourne.”

Victoria has called in hundreds of health workers and Australian Defence Personnel from Queensland, South Australia and Western Australia to help combat the virus spread.

“It is challenging, heart-breaking. It is very, very difficult but these are the appropriate public health measures,” Mr Andrews said.

“But ultimately, if I didn’t shut down those postcodes, I would be
shutting down all postcodes. And we don’t want to get to that point.”

Elsewhere, local mayors are furious at reports that up to 1000 people have refused coronavirus tests and are concerned for the welfare of local residents and businesses.

“It makes me feel incredibly angry,” Sarah Carter, the mayor of the inner-west city of Maribyrnong, one of Melbourne’s hotspots, told the Nine network on Wednesday.

“I just think it’s the height of entitlement, to be honest, not to take the test and I would urge everyone in our community, when asked, to take that test.”

Cr Carter said she hoped residents would unite to support one another.

“This is our community, it is our local economy, they’re local mums and dads running these small businesses and they have done it so bloody tough,” she said.

In the city of Hume, which covers some of Melbourne’s outer north-west suburbs, mayor Carly Moore said she was devastated.

“It’s been a tough time for our community, we were starting to see some signs of hope, we were starting to get really optimistic about what the future might look like, and realistically, we’re right back to square one,” she said.

Ms Moore was also angered by people refusing tests.

“Everybody needs to do their bit,” she said.

“There’s no reason why everybody in our community can’t pull their weight and get the test.”

Testing Broadmeadows, a suburban hotspot in Melbourne. Photo: Getty

About 54,000 homes have been reached and 113,000 people tested in the week since a door-knocking blitz started in affected suburbs last Thursday.

But there are some optimistic signs, even among the bleak figures. Mr Andrews said Wednesday’s new cases were mainly in already identified hotspot suburbs.

“There is the beginnings of some consistency here,” he said. “That is obviously better than other options where we might see doubling and doubling again.”

Prime Minister Scott Morrison has backed the drastic measures.

“Where outbreaks do occur you need to move on them, as the Victorian government is and they have our full support with that,” he said.

Victoria has also launched an inquiry into hotel quarantine. It will be led by a retired judge.

Cases on Wednesday

• Five more staff linked to the Al Taqwa College cluster (total eight);
• Two more cases in the Stamford Plaza outbreak (total 31);
• One new case linked to the North Melbourne outbreak (30);
• One new case linked to the outbreak at the Coles distribution centre in Laverton (six)
• Three new cases linked to cases associated with Hugo Boss in Collins Street, Melbourne;
• A healthcare worker at the Joan Kirner Women’s and Children’s Hospital;
• A healthcare worker at Epworth Hospital;
• A staff member at SBS Radio in Melbourne;
• Students at three new schools – Hoppers Crossing Secondary School, Creekside College in Caroline Springs and Aitken Creek Primary in Craigieburn;
• A staff member at Westbreen Primary School in Pascoe Vale.
• Two positive cases at the Maple Early Learning Centre in Mernda.

-with AAP