Riot police fire tear gas at youths throwing missiles in central Athens as an otherwise peaceful demonstration against cuts continues Reuters

Greece is facing major disruption on Tuesday as unions begin a 48-hour general strike before a parliamentary vote on harsh austerity measures demanded in return for international rescue loans.

Protest rallies in Athens are due to converge on parliament as industrial action called in protest against tax hikes was expected to disrupt or halt most public services.

More than 5,000 police have been deployed to guard central Athens where anti-austerity demonstrations earlier this month ended in scenes of violence as protesters clashed with riot officers.

"We expect a dynamic and massive participation in the strike and the march to the centre of Athens. We will have 48 hours of working people, unemployed, young people in the streets," Spyros Papaspyros, leader of public sector union ADEDY, told Reuters.

Doctors, paramedics, journalists, postal workers and private sector employees were all expected to join the protest. Stoppages by Greek air traffic controllers are likely to disrupt flights and ferry departures from Athens are also expected to be hit.

The unions are angry that the proposed austerity package would raise taxes on minimum wage earners and other Greeks in addition to earlier cuts that have driven unemployment past 16%.

Parliament must approve and implement the programme this week if Greece is to receive a scheduled bailout loan of €110bn from the European Union and the International Monetary Fund. Without the loan Greece risks becoming the first eurozone country to default on its debts – an event that could trigger a crisis in other economically weak European countries and have major global consequences.

"These measures are a massacre for workers' rights. It will truly be hell for the working man. The strike must bring everything to a standstill," Thanassis Pafilis, a member of parliament for the pro-strike Greek Communist party, told Associated Press.

The three-day parliamentary debate over the austerity package came as France, among eurozone nations scrambling to prevent a default, suggested rolling over some Greek debt for 30 years.

The proposal by the French president, Nicolas Sarkozy, offered hope to Greece's socialist prime minister, George Papandreou, before the debate.

"I call on you to vote for survival, growth, justice, and a future for the citizens of this country," Papandreou told politicians.

Unable to offload its sovereign debt, Greece is dependent on bailout loans and is banking on a new rescue package to cover a 2012 financial hole. Although any further assistance is likely to be dependent on approval of austerity measures, Papandreou said he hoped the terms of a second bailout would be better than the first.

"I call on Europe, for its part, to give Greece the time and the terms it needs to really pay off its debt, without strangling growth, and without strangling its citizens," he said.

Theodoros Pangalos, the deputy prime minister, rejected suggestions Greece might be forced to abandon the euro and return to its old currency, the drachma.

"There would be riots everywhere, shops would have empty shelves and people would be jumping out of windows ... It would also be disastrous for the entire economy of Europe," he told the Spanish daily El Mundo.