Greece's opposition has urged Prime Minister Alexis Tsipras to call off a referendum on July 5 and "stop the destruction", media reported on Tuesday.
The July 5 referendum is a result of the creditors offering joint proposals to the Greek side last week, which Greece rejected and termed as humiliating.
"We will not become beggars in the Balkan neighbourhood. The 'yes' to Europe will win," Stavros Theodorakis, leader of the opposition party, To Potami, said on Monday.
"We call on Tsipras to find the courage to tell the Greek people the truth. To set aside opportunism. To withdraw the referendum and enter into an agreement with the Europeaan Union," the Athens-Macedonian News Agency (ANA - MPA) quoted him as saying.
Theodorakis' appeal came ahead of the expiry of Greece's bailout plan on Tuesday, the same day it faces a deadline to repay a 1.6 billion euros ($1.7 billion) to the International Monetary Fund (IMF).
However, Tsipras urged Greece's voters to reject the creditors' proposals, saying this would give Greece "more powerful weapons" to take to the negotiating table, BBC reported.
"We ask you to reject it with all the might of your soul, with the greatest margin possible," he said on Monday evening.
Tsipras also hinted strongly that he would resign if the result of the referendum was a "yes" vote.
"If the Greek people want to proceed with austerity plans in perpetuity, which will leave us unable to lift our head... we will respect it, but we will not be the ones to carry it out," he said.
Tens of thousands of people gathered outside the Greek Parliament House in Athens on Monday evening in a show of support for the government's proposals.
A rival protest organised by those calling for a 'yes' vote is due later on Tuesday.
Meanwhile, European Commission President Jean-Claude Juncker said he felt betrayed by the Tsipras-led government and called on Greek voters to oppose him.
Juncker said he still believed a Greek exit from the eurozone was not an option and insisted that the creditors' latest proposals meant more social fairness.
The government on Monday ordered all banks to be closed until July 6 after the European Central Bank (ECB) decided not to extend its emergency funding.
The ECB is believed to have disbursed virtually all of its ceiling for funds, amounting to 89 billion euros (about $99 billion).
Long queues of people were seen outside ATMs, with withdrawals capped at just 60 euros ($66) a day.
Elderly people, many without bank cards, were seen waiting outside closed bank branches in the hope of getting access to funds.
The Athens stock exchange has also been closed as part of the emergency measures.
The government said it would make public transport free in the Athens area for a week while the banks are closed.
