Scott Morrison has warned that the national economy will take another hit from the extended Victorian lockdown as he took aim at the state’s roadmap for easing restrictions, saying leaders “cannot create a burden that is too great to bear”.

The prime minister refused to specify on Monday whether the federal government would rethink its plan to reduce the rate of the jobkeeper and jobseeker programs this month, calling on the Victorian government to spell out its own economic support package before Canberra considered taking action.

But Morrison raised questions about Victoria’s contact-tracing capabilities and said he hoped the plan unveiled by the premier, Daniel Andrews, was the “worst-case scenario” and only a “starting point” for managing the virus in the weeks ahead.

Facing reporters in Canberra on Monday, Morrison said the assumptions needed to be “interrogated” by the federal government and health experts because the plan would have “very severe impacts”.

The prime minister said Sydney would be under curfew right now if the thresholds set in the Victorian plan were extended to New South Wales.

“Sydney doesn’t need to be under curfew now [because] they have a tracing capability that can deal with outbreaks,” Morrison said.

“That’s why I say it’s important that we work on building that tracing capability in Victoria, to get it at a level that enables it to move in a more confident way than I think the plan that was announced yesterday set out.”

Andrews later rejected the comparison, telling ABC’s 7:30 it was not “particularly valid” and nor was it “worthwhile”.

“Sydney has not had the amount of community transmission we’ve had,” Andrews said.

“It is difficult to make comparisons with other states, because in many respects, the circumstances we face … the challenge that we face is very, very different.”

The former prime minister Malcolm Turnbull also leapt to Andrews’ defence, saying the premier had “a very difficult job”.

Earlier, Morrison said the commonwealth did not have the authority “to step in and tell the Victorian government they have to follow another plan” but would provide “constructive feedback” after sitting down with business and industry groups.

His comments come as federal Coalition MPs and senators have been sharpening their attacks on the Victorian government’s handling of the second wave of infections.

The Liberal senator James Paterson told Sky News that Victorians were entitled to be angry about the lockdowns, which were “only being imposed on them because of the failures of the Daniel Andrews administration” – pointing to contact-tracing and hotel quarantine problems.

The former Nationals leader Barnaby Joyce went on Seven’s Sunrise program to denounce state premiers more generally for imposing border restrictions that were “causing massive damage” and splitting Australia into “all these separate countries”. Joyce also made a passing reference to “civil war” as he questioned how the border dispute may be resolved.

The federal opposition’s health spokesperson, Chris Bowen, rebuked Joyce and other Coalition politicians for second guessing the health advice and appointing themselves as “shadow chief health officer of Victoria”.

“Liberals can try and make a name for themselves beating up on state governments but that is not a ‘team Australia’ approach,” he said.

Bowen also warned the government that there was “a long way to go in the Morrison recession” and that withdrawing economic support “on an unrealistic timeframe could do great economic damage”.

Sentiment has been building within Coalition ranks that state governments have felt free to impose tough border restrictions and other strict health measures because of the backup provided by the federal government’s flagship economic support programs.

About a month ago federal Treasury forecasts indicated that the lockdown in Victoria would be likely to push unemployment in Australia to 10% by the end of the year, and would cost the national economy between $10bn and $12bn.

Morrison said Treasury would update its forecasts about the economic impact as part of the process of preparing the budget, which is due for release next month, but there was no doubt that it would have a negative impact on joblessness, incomes and revenue.

He said while the biggest impacts would be in Victoria, there would be “domino impacts” elsewhere because of the role that the state played in the national economy through supply chains.

Asked how he could justify slashing the jobkeeper and jobseeker payment rates at the end of this month, given the ongoing restrictions on work and life in Victoria, Morrison emphasised that the programs were being extended beyond the initial September deadline.

Labor has signalled it will continue to argue against the tapering of jobkeeper down from $1,500 a fortnight to $1,200 in September, then $1,000 in January, but the rate is not dealt with in legislation that passed last week.

The prime minister called on the Victorian government to outline what programs it would roll out at a state level to “mitigate the economic impact of the decisions the Victorian government has made”.

“I’ll be looking to see what they’ll be doing first before the commonwealth considers any responses that we’ll be making,” he said.

Prof Brendan Murphy, the secretary of the federal health department, said some of the assumptions in the Victorian roadmap appeared to be based on “a very conservative approach”.

But Murphy said he had no reason to believe Victoria was now pursuing an elimination strategy. The strategy remained “aggressive suppression”.

Morrison insisted that he understood the need to avoid a relapse in infection numbers in Victoria but said governments managing the pandemic needed to take care to generate and maintain community support for the plans.

“We cannot create a burden that is too great to bear, because that would see all the plans fail if that were the case,” he said.

Morrison was joined by Murphy and the federal health minister, Greg Hunt, to announce vaccine manufacturing deals that were foreshadowed overnight.