Greece is teetering on the edge of collapse with its society at risk of disintegrating unless the country's near-empty public coffers are shored up with urgent financial aid, the country's prime minister has warned.

Almost three years after the eruption of Europe's debt drama in Athens, the economic crisis engulfing the nation has become so severe that democracy itself is now imperiled, Antonis Samaras said.

"Greek democracy stands before what is perhaps its greatest challenge," Samaras told the German business daily Handelsblatt in an interview published hours before the announcement in Berlin that Angela Merkel will fly to Athens next week for the first time since the outbreak of the crisis.

Resorting to highly unusual language for a man who weighs his words carefully, the 61-year-old politician evoked the rise of the neo-Nazi Golden Dawn party to highlight the threat that Greece faces, explaining that society "is threatened by growing unemployment, as happened to Germany at the end of the Weimar Republic".

"Citizens know that this government is Greece's last chance," said Samaras, who has repeatedly appealed for international lenders at the EU and IMF to relax the onerous conditions of the bailout accords propping up the Greek economy.

Mounting anti-austerity rage before a new round of sweeping EU-IMF-mandated austerity measures appears to have caught the government off-guard, with officials voicing fears over the ability of Samaras's fragile coalition to survive.

The unprecedented storming of Greece's defence ministry by hundreds of protesting dockworkers on Thursday – a breach of security not seen in modern times – has especially unnerved officials. On Friday, Samaras lashed out at "those who don't understand the meaning of law and order".

"The government is waging a battle on all fronts for the nation's credibility and its future so that the sacrifices made by Greeks aren't lost," he said, referring to the spending cuts and tax increases that have sparked record levels of poverty and unemployment. "I will not allow the country to become a free-for-all."

Many officials fear the conservative-led alliance is being pushed too far in negotiations that have dragged on for weeks over the latest €13.5bn package of austerity measures that is the price of further aid. Growing speculation that Greece will be kept waiting until after the US elections in November before it receives its next disbursement of aid has added to the pressure. On Friday EU officials made clear it was highly unlikely a decision would be made on the payment – vital to kickstarting the cash-starved economy – at an upcoming EU summit on 18 October. The Athens government is also appealing for a two-year extension of the debt-choked country's fiscal adjustment programme in an effort to ameliorate the impact of further punishing austerity.

In the interview Samaras emphasised that Greek cash reserves would run dry by the end of November. "The key is liquidity," said the leader. "That is why the next credit tranche is so important for us."

The high-wire act of placating international lenders while keeping social unrest at bay will be tested as never before when Merkel, the German chancellor, flies into Athens next Tuesday. With anti-EU sentiment at an all-time high, opposition parties and trade unions vowed a baptism of fire.

"She should expect demonstrations. Greek society will welcome her with mass protests," said Panos Skourletis, a spokesman for the radical left main opposition Syriza party.

The Independent Greeks party, also vehemently anti-bailout, has said it will make war reparations a major part of its own protest when it stages a "symbolic blockade" outside the German embassy in Athens during Merkel's visit.