“It is a holiday today, because the democracy is a celebration and happiness. Democracy defeats fear and blackmail, and then liberation comes,” Tsipras told the crowd.
“I am very optimistic,” he added.
Tsipras proposed to hold a referendum on Greek bailout in June, after the country’s negotiations with international creditors came to a standstill.
Tsipras has urged the voters to say a "proud no" to the EU ultimatums, arguing that the option would strengthen the country's negotiating position.
Greek national debt stands at about $350 billion, of which $270 billion is owed to the European Central Bank (ECB), the International Monetary Fund (IMF) and some Eurozone countries.
Media suggested that if Greek people vote “Yes” in a Sunday referendum, Tsipras would most likely have to step down. Greek Finance Minister Yanis Varoufakis has already pledged to resign if this scenario unfolds.
In case Greece votes “No,” it would be interpreted as a step toward the exit from the Eurozone, according to Eurogroup President Jeroen Dijsselbloem.