Victoria is at the “tipping point” of the latest Delta outbreak, and health authorities warn the state could be locked down for months if new clusters continue to emerge amid a rise in mystery cases.

Concern is mounting over clusters spread across the city after eight major outbreak sites emerged in just over a week.

Contact tracers are now racing to connect five new mystery cases recorded on Sunday to existing clusters across Caroline Springs, Melton, Middle Park, Richmond, and Maribyrnong.

Covid-19 commander Jeroen Weimar said Victoria was at a “tipping point”.

“Our concern today is that we’ve done a really good job with the communities around the schools, around the shopping centres out west, around the footy club, a number of other community groups. Those numbers are pretty stable, and they’re all contained,” he said.

“That’s why this is a real tipping point.”

Thirteen of the 25 new infections announced on Sunday were out in the community while infectious, with active cases across the state rising to 185.

“I don’t know what our position will be on Thursday, but these are not good signs,” he said. “There are a number of mystery cases and those numbers continue to grow and that is really challenging. These numbers are too high.”

Mr Andrews said stay at home orders could remain in place for months if needed to prevent cases from snowballing like in NSW, which recorded 415 new local cases on Sunday. “The choice really is between where we are now and hundreds and then thousands of cases,” Mr Andrews said, adding that the strategy was to avoid the situation in NSW where hundreds of thousands of extra vaccine doses are needed after lockdowns and contact tracing failed.

“I’m determined to make sure that it doesn’t happen here. I know no one’s enjoying this. But what’s worse than this is, well, being locked up till the end of October, or indeed the end of November because that’s how long it may well take to get 80 per cent of people through the vaccination program,” Mr Andrews said.

Mr Andrews said Victoria was “running alongside” the state’s outbreak but had to drive cases down before figures spiralled out of control and the healthcare system became overwhelmed.

Four Covid-infected Victorians are in hospital, including one in intensive care.

Young people appear to be fuelling the spread of the virus, as new figures reveal that 83 people aged under 19 are infected.

Across the state, 44 children under 10 and 39 youths aged between 10 and 19 are infected with the virus.

Sixty-five people aged 20 to 40 years also have the virus.

“We’re dealing primarily with people in their 20s, 30s and 40s, they’re quite an active group, lots of social contacts, lots of clubs and lots of ­exposure sites,” Mr Weimar said.

Apartment block residents in St Kilda East, Glenroy and Carlton were also told to get tested and isolate at the weekend after being linked to the current outbreaks.

More than 500 exposure sites have been identified, including dozens of tier one and two sites across inner-Melbourne suburbs that were added on Sunday.

Opposition Leader Michael O’Brien on Sunday called for the Premier to tell Melburnians when the lockdown would end.

“It is certainly not the short, sharp circuit breaker we were all hoping for,” he said.

“We just want the Premier to be upfront with us, tell us how much longer he thinks we are going to be locked down for and what those conditions will be.”

NSW TO BE CUT OFF FROM REST OF NATION

New South Wales is expected to be isolated from the rest of the country for months to come, as state leaders acknowledge its lockdown will never drive case numbers back to zero.

The worsening outbreak could throw into chaos the national cabinet’s agreed plan to reopen Australia, because it assumed there would be only small number of Covid-19 cases when the vaccination targets of 70 per cent and 80 per cent were reached.

The state recorded 415 cases on Sunday as Gladys Berejiklian said it was “not possible to eliminate it completely”.

“The best chance we have to live with it freely and safely is to get the case numbers down as low as possible,” the NSW Premier said.

Victorian Premier Daniel Andrews agreed, saying there was “no way they’re going to get to zero cases”.

“Nothing else they’re doing is working … This is where they’re at now, they’re going to have to vaccinate their way out of this,” Mr Andrews said.

He said there was “no doubt” about the national cabinet’s plan to end lockdowns and reduce restrictions among state and territory leaders.

“No one’s walking away from the plan,” Mr Andrews said.

But senior federal government sources said that for the national cabinet plan to succeed, they expected states would keep their borders closed to NSW for months, and possibly until Christmas.

Mr Andrews said that if Ms Berejiklian reopened her state at the 80 per cent threshold, and there were still many cases of community transmission, then “they’ll be locked out to here”.

He said the Doherty Institute modelling underpinning the national cabinet plan was based on Australia reaching the vaccination thresholds while having successfully suppressed the virus.

“That modelling does not assume that there are thousands of cases, and hundreds of cases every day,” Mr Andrews said.

“If we want to be open, if we want to have a new set of rules as we go into a new year, if we want to preserve our health system for everyone who needs it … then when we get to 70 and 80, we have to have cases down here, not raging.

“Otherwise I don’t know how that works.”

Mr Andrews maintained that was why it was paramount that Melbourne’s continuing lockdown was successful, because the city and state could not reopen if it had thousands of cases, even with 80 per cent of people over 16 fully vaccinated.

“I’m determined to make sure that it doesn’t ­happen here,” Mr Andrews said.

With all of NSW now in lockdown, chief health officer Kerry Chant said on Sunday: “I cannot stress enough the seriousness of the current situation, and my grave concerns that these case numbers will continue to escalate.”

DOUBLE HIT FOR SICK BOY

A smiling teen dealt a deadly double blow – Covid-19 and meningitis – was fighting for his life in hospital on Sunday night.

Osama Suduh, 15, is from Sydney’s southwest, which continues to be the epicentre of that state’s Covid-19 outbreak.

But authorities confirmed on Sunday that although the teenager tested positive for the virus, the reason for his admission was because he had pneumococcal meningitis.

The devastating case came as NSW recorded 415 new local infections of Covid-19 and another four people died.

Authorities confirmed 381 cases were in hospital, with 62 in intensive case and 55 of them were unvaccinated, while seven had received their first dose of the vaccine.