By Matina Stevis and Andrea Thomas 

At newspaper kiosks in Greece, ahead of Sunday's referendum, some front pages this week showed swastikas and the word "OXI", Greek for "no." On the streets of Athens, a poster showed German Finance Minister Wolfgang Schäuble with the words: "He's been sucking your blood for five years. Now tell him NO."

In Germany, Greece's most powerful creditor, the press have this week poured their own contempt and ridicule on Greek Prime Minister Alexis Tsipras, with epithets ranging from "extortionist" to "gambler" and "coward." Germany's mass-circulation tabloid Bild thundered on Friday that Greek Finance Minister Yanis Varoufakis "belongs in a cabinet of horrors, but not in Europe." German public opinion has thus turned more hostile than ever to lending Greece more money to keep it in the euro.

Whatever the outcome of Greece's vote Sunday on whether or not to accept their international creditors' demands for more austerity measures, tensions between Greeks and Germans over the debt crisis have now erupted into open displays of frustration and resentment that won't die down quickly.

Many Germans, from voters to the highest levels of government, have lost patience with what they see as Greece's efforts to blackmail Europe into subsidizing an inefficient Greek economy and public sector that refuses to adapt to the competitive realities of eurozone membership and globalization. Whereas many Germans viewed past Greek governments as corrupt, they see Mr. Tsipras's coalition, led by the left-wing Syriza party, as reckless.

German newspaper Handelsblatt played on Mr. Tsipras's image as an irrational would-be extortionist on Friday, covering its front page with a montage that showed the Greek leader holding a gun to his own head. "Give me money or I'll shoot," the caption said.

Many Greeks across the political spectrum believe Germany was the driving force behind a bailout program that was unworkable, imposing an overdose of austerity, and turning a financial crisis into a full-blown depression. Resentment at German pressure on Greece to adopt more of the same economic recipe--while Berlin blocks all international discussion about restructuring Greece's crushing debt--is the main reason why about half of the Greek electorate is expected to vote "no" to creditors' bailout terms on Sunday, despite the awareness that such a vote risks a cataclysmic Greek exit from the euro.

Mr. Schäuble, Germany's irascible finance chief, has become the leading European hate figure for many Greeks, drawing more scorn than Chancellor Angela Merkel. Many Greeks blame Mr. Schäuble personally for the deep cuts to Greece's social safety net since 2010.

"He took half my pension and I was working for 32 years," said 80-year-old Niki Skoulioti of Mr. Schäuble, while queuing at an ATM in Athens. "There's no way I will continue to accept him telling us what to do," she said. "I'm voting 'no' on Sunday."

"The Germans want us under their boot," said Nikolas Marianis, a 76-year-old farmer in Dervenakia, a village near Corinth known as the site of a key battle in Greece's war of independence against the Ottoman Empire in 1821, and where a spirit of nationalist resistance against foreign powers is still strong today.

"We won't surrender. Greeks have always held their head up high, especially against" the Germans, Mr. Marianis said. His wife, Maria, nodded her head and chimed in: "This is a country of heroes. We're not going to become slaves."

"If you ask most Greeks they will tell you that the Germans, especially Ms. Merkel and Mr. Schäuble, are seeking to reduce us to a debt colony," says Theodore Couloumbis, emeritus professor of politics at Athens University. He says Syriza is capitalizing on anti-German sentiment.

"Syriza has been more or less using these slogans of "debt colony" to explain its analysis: that a group of highly conservative leaders in Germany--primarily Merkel and Schäuble--are responsible for Greece's troubles: 26% unemployment, massive recession, and so on. Their argument is that we cannot afford to go along with these people and we have to stand up and be sovereign, heroic, dignified," Mr. Couloumbis says.

Syriza and its coalition partner, the right-wing nationalist Independent Greeks, have had Germany in their rhetorical cross hairs since coming to power in January.

"This is the Europe of German domination," Independent Greeks leader and Greek Defense Minister Panos Kammenos told his country's parliament last week, his voice shaking and eyes tearful. "The great 'no' [by the government to creditors' demands] was the political decision against the misery of an entire nation."

The barrage of anti-German rhetoric from Greek politicians has undermined popular and parliamentary support in Germany for continued bailout loans for Athens.

The influential BDI Federation of German Industry signaled this week it has all but written off Greece as a eurozone member. In a statement, BDI President Ulrich Grillo said: "Greece cannot be maintained in the currency union at any price," adding that the cost of an exit would be high for Greece but "limited" for Germany.

In Berlin's corridors of power, even veterans of eurozone bailouts are finding it hard to hide their loss of patience with Greece. Frank-Walter Steinmeier, Germany's soft-spoken and famously patient foreign minister, said he was "somewhat stunned at what we have witnessed in the past few days, from the Greek government, and especially from Prime Minister Tsipras."

Fellow Social Democrat Carsten Schneider and his party's deputy parliamentary floor leader, said on Monday: "More damage is probably being done this week than in the past five years," and blamed this on the Greek government.

The most bitter venom came from conservative ranks, with Wolfgang Bosbach, a longtime opponent of eurozone bailouts, calling the referendum "politically irresponsible" and fellow lawmaker Gunther Krichbaum saying "Mr. Tsipras has lost touch with reality."

An opinion poll by Infratest Dimap for public broadcaster ARD published on Friday showed 68% of Germans blame the Greek government for the escalation of the debt crisis, with only 4% pointing the finger at other eurozone countries. The poll of 1,501 voters was conducted from June 29 to July 1 and had a margin of error of 1.4% to 3.1%.

In a separate Forschungsgruppe Wahlen survey for public broadcaster ZDF on Thursday, 85% of Germans said Europe was right not to have made more concessions to the Greek government. The poll of 1,234 respondents was conducted from June 30 to July 2 and had a margin of error of 2% to 3%.

Yet both polls showed Germans remained ambivalent about Greece's future in the eurozone, with those advocating its continued membership and those favoring an exit from the currency union roughly in balance.

"I think Greece should leave the euro. It would be better for Greece given how things there are at the moment," said 33-year-old Berlin Marco Otto.

Thomas Heblich, a 29-year old bookseller in Frankfurt, said Greece "should never have been part of [the euro]. Without question, they fudged the numbers."

There are still pockets of sympathy for Greece though. "It's undiplomatic what the Greek government is doing, but perhaps it doesn't have any other choice," said Werner van Alen, a 65-year-old retired teacher from western Germany. "Germany received help sixty years ago. We as Germans have a moral obligation to help."

Bertrand Benoit in Berlin contributed to this article.

Write to Matina Stevis at matina.stevis@wsj.com and Andrea Thomas at andrea.thomas@wsj.com