Clashes between rival groups of protesters broke out in front of the Greek parliament on Thursday, interrupting a rally by tens of thousands against a tough new package of austerity measures due to be approved later in the evening.
Police stood by as hundreds of black-clad youths hurled stones and petrol bombs at demonstrators from PAME, a communist-affiliated labor group which has traditionally favored well-organized and peaceful protest rallies.
At least six injured could be seen receiving treatment from volunteer first aid workers.
The mood among the crowd, estimated by police at more than 60,000 had been peaceful until the disturbance in front of the luxury hotels lining Syntagma Square.
The clashes followed violence on Wednesday when groups of young protesters fought police at the start of a 48-hour general strike against the package of cuts and tax hikes required by the European Union and International Monetary Fund.
Deputies are expected to pass the plan late on Thursday after the bill passed a first vote on Wednesday.
As Prime Minister George Papandreou prepared to fly to Brussels where a meeting of European leaders on Sunday will try to agree measures to stem the debt crisis, ministers made a final plea to pass the bill and prove Greece's credibility.
You have to approve the law, with all its clauses, Finance Minister Evangelos Venizelos told lawmakers. This is not a game. If anybody thinks they can test how much wiggle-room we've have, they're mistaken.
A vote is expected late on Thursday but no precise time has been set.
After last minute arm-twisting from party bosses, two potential rebel deputies swallowed their objections and said they would vote to pass the bill but said they could accept no more austerity.
I will vote in favor, but this is the last time -- I am struggling with my conscience, said Vasso Papandreou, a member of PASOK who is no relation to the prime minister.
Enough is enough, society is despairing, the country is collapsing, she said to applause from other PASOK deputies.
With only one rebel deputy still holding out, the government's majority of 154 seats in the 300-member parliament is expected to pass the bill which Athens needs to convince international lenders to continue their support.
But the mix of public sector pay and pension cuts, tax hikes and changes to sectoral wage agreements has roused deep hostility from many Greeks, who say it punishes the weak and will only drive the stricken economy further into the ground.
The general strike called by unions representing around half the Greek workforce is one of the largest protests since the start of the crisis two years ago and brought more than 100,000 people to the streets on Wednesday.
The unrest that broke out during the rally left central Athens covered in smoldering rubbish and lumps of masonry hacked off buildings in a repeat of clashes seen in anti-austerity protests in June.
The mood remained hostile to both the government and the EU-IMF Troika, which is expected to approve a new tranche of aid but which has pressed for tougher action from the government.
A spokesman for GSEE, the main private sector union, said strike levels had fallen somewhat on Thursday, as many cash-strapped workers, who lose pay for stoppages, returned to work but protesters said they were determined to continue.
I will be protesting every day, it's a matter of survival. They must go, said 49-year old Yannis Zahariadis, a civil servant and father of four. I was forced to borrow money from my mother, a pensioner, to make ends meet.
Wednesday's violence, which appeared to be the work of a hardcore group of mainly younger protesters, overshadowed the first day of the strike that shut down much of the country and drew in Greeks from broad sections of society.
On Thursday, shops re-opened but ministries, schools and other public buildings were shut, transport services severely restricted and hospitals running on skeleton staffing.
As the protests have continued, there has been widespread speculation the government will fall early, forcing a snap election before the scheduled date in 2013 but Papandreou has repeatedly ruled out stepping down early.
People sent a message on Wednesday that they have reached their limits and can't take any more austerity, said Theodore Couloumbis of the ELIAMEP think-tank.
With Greece reeling after three years of recession and immobilized by a mountainous public debt, the government is under growing pressure, trapped between international lenders demanding tougher action and growing public anger at the cuts.
The bill due to be approved on Thursday foresees an average wage cut of about 20 percent for public sector workers, bringing total income losses since the crisis started two years ago to about 40 percent.
There were smaller protest rallies in other cities across the country but the government vowed to push through the measures, which are needed to obtain the aid it needs to keep paying the country's bills.
Today, we must arm the prime minister for negotiations that will decide if Greece can pay for wages and pensions, fuel and pharmaceuticals, whether it can continue as an EU member, Education Minister Anna Diamantopoulou told parliament.
(Additional reporting by Lefteris Papadimas; Writing by James Mackenzie; Editing by Sophie Hares)