Greece's left-wing government, led by Prime Minister Alex Tsipras, and its opponents battled for the backing of the nation Friday ahead of Sunday's referendum, a vote that could change the future of the country and have far reaching implications across Europe.

Opinion polls suggest Greeks are split between Tsipras's call to vote no to austerity demands set by creditors negotiating with Greece for a bailout agreement, and those calling for a "yes" to the terms of a deal, The Wall Street Journal reported.

 “I call you to say again a big proud ‘no’ to ultimatums on Sunday,” Tsipras told a crowd police estimated at more than 20,000 people, who waved the flags of Greece and the left-wing Syriza party.

A short distance away, another approximately 20,000 people gathered to back the "yes" campaign, waving the European Union and Greek flags, along with colorful "yes" signs, the Journal reported

“Greece, Europe, democracy,” they chanted.

However, analysts say no matter what the Greeks decide in the vote, the government’s hold on power is more uncertain than its prime minister suggests.

A win for the No campaign could allow Tsipras to get a stronger grip on power. However, analysts told The Associated Press they don’t think that could be the case.

They say a “no” note could still plunge Tsipras’ position into uncertainty if negotiations drag on with creditors who see such the outcome as a Greek snub of the euro. Without a quick deal, banks could stay closed to keep their reserves from running dry.

"A deteriorating import-dependent economy will provoke a rapid decline in public support for the government and fresh elections may become inevitable, but this will take time," said Dimitri Sotiropoulos, political science professor at the University of Athens.

A vote for the Yes campaign could case Tsipras’ public mandate in doubt and force him to broaden his coalition government, political analyst George Sertzis said. The never government may have Syriza at its core, but the cabinet’s composition could change to include “respected personalities who can be recruited to fill that role.”

The radical left Syriza emerged from the political fringes in January as Greek voters sought an alternatives to what they saw as a bankrupt political establishment they blame for opening the door to half a decade of punishing salary and pension rollbacks, steep job cuts and hefty taxes.

Just a few years ago, the country's two main political forces, the right-wing New Democracy and the socialist PASOK parties, commanded some 80 percent of the vote between them. Now, with many Greeks seeing them as kowtowing to the lenders' diktats, their support was dwindled.

Tsipras' youth, unorthodox style and pledges to fight the good fight for the country's poorest endeared him to many and persuaded some that he could take on the institutional behemoths that decide the economic fate of entire nations.

However, the lack of results in Greek talks have diminished the government’s credibility in the eyes of Europe’s power circles.

"This government doesn't trust the institutions of the EU and the IMF, and those institutions trust the Greek government even less," said Sotiropoulos.

Tsipras’ gambit appears to rest on whether he can clinch a deal quickly so that banks can reopen and get money flowing to businesses once more. Tsipras told private TV station Antenna Thursday that he sees a deal emerging with lenders “within 48 hours” after the referendum.

His finance minister, Yianis Varoufakis, told Ireland's RTE radio Friday that an agreement with creditors "is more or less done" and that European officials had put forward "very decent proposals" this week.

The European Union and International Monetary Fund are unlikely to cave in on demands for tough austerity measures, notes Sotiropoulos.

The creditors may offer a vague pledge to consider restructuring Greece’s crushing debt, but that won’t likely happen until the government faithfully implements the terms of the deal for at least 12 to 18 months, said Sotiropoulos.

A 'no' win would be a Pyrrhic victory for the Greek government. You can't survive on Pyrrhic victories because you need funds to keep the country running," he said.

Sefertzis said Tsipras' political decline may come much faster even with a referendum "no" in his pocket as he would have little time to get to keep the country from economic collapse.

With the economy fledgling, Tsirpras’ hold on power would be a “matter of days rather than weeks,” said Sefertzis.

Writing in the liberal daily "Ta Nea," pollster Elias Nikolakopoulos said any predictions about the outcome on Sunday "are exceedingly precarious" because party allegiances in this vote are fluid.

Speaking on Ireland's RTE radio, Varoufakis even suggested that a "yes" win is possible, albeit by a narrow margin. But even then, he insisted his party would come out "stronger and united."

"Syriza will remain the only credible party in the parliament, our young leader will remain the only credible leader of this nation," Varoufakis said.

The Associated Press contributed to this report