A Victorian man in his 20s has died of coronavirus, becoming Australia’s youngest victim of the pandemic yet.

The man was one of 14 more fatalities and 372 new infections confirmed by Premier Daniel Andrews on Friday.

The others who brought Victoria’s virus death toll to 289 were three women and two men in their 80s, and four women and four men in their 90s.

The national virus toll is 375.

Twelve of the fatalities confirmed on Friday were linked to the crisis in Victorian aged care.

Until Friday, Australia’s youngest coronavirus victims were two men in their 30s who died in Victoria in late July and early August.

Friday’s grim news came as Mr Andrews and chief health officer Brett Sutton expressed concern about the ever-growing number of mystery cases among the state’s virus infections.

The state has 3119 COVID cases that cannot be traced – up 51 from Thursday. The origins of up to 20 per cent of infections in Melbourne and 13 per cent in country Victoria remain a mystery – although Professor Sutton said the numbers were stabilising as the state’s overall infections slowed.

“Stage 4 will only show in the numbers over the next few days,” he said.

“These [Victorian figures] are still the effect of mask wearing and Stage 3, so that is encouraging. We’ve turned the corner with those interventions and we should see a further driving down to transmission with Stage 4 restrictions so it is going on the right direction and I’m confident we’ve seen the peak but it’s got to come down quickly.”

Friday’s daily figures came after Victoria had its lowest number of new cases in weeks on Thursday, with 278 infections and eight fatalities.

Elsewhere, NSW confirmed another nine COVID infections on Friday, including one at the Tangara School for Girls in Cherrybrook.

The cluster at the school has grown to 21, with its source still a mystery.

The cluster at Tangara School for Girls now numbers 21.

St Vincent’s College in Potts Point became the third independent Catholic school in Sydney to close on Friday after a student’s positive test to COVID-19.

Our Lady of Mercy College in Parramatta and the Tangara school are both closed until August 24.

On Thursday, NSW had its first death since August 1 after a Sydney woman in her 80s was linked to the Our Lady of Lebanon Church cluster.

She was the state’s 53rd coronavirus fatality.

Across the Tasman, New Zealand’s COVID outbreak has grown to 30, with more cool store workers and two people in a town 200 kilometres from Auckland all confirmed with the virus.

Six workers at the Americold cold storage facility in suburban Mount Wellington have now tested positive to the virus.

Two of the other cases are from the Waikato town of Tokoroa, more than 200 kilometres south of Auckland. There is another probable infection there too.

One of those people is linked to the South Auckland family where the outbreak began.

New Zealand has 48 active coronavirus cases – all of the others are returned travellers in mandatory quarantine.

A meeting of the NZ cabinet is scheduled for Friday afternoon.

Extending Auckland’s COVID-19 lockdown and possibly delaying the looming national election will be top of the agenda.

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Meanwhile, a testing blitz began in regional Victoria on Friday morning as the state government attempts to rein in new cases.

Geelong (167 active cases), Ballarat (25) and Bendigo (56) have been identified as sources of concern after steady growth in infections in the past fortnight.

On Thursday, Mr Andrews said more data would develop a “clearer picture” of the outbreaks, while deputy chief health officer Allen Cheng hoped it would “obviate the need for Stage 4” in the regional centres.