Rioters hurled petrol bombs at police who responded with tear gas as an anti-austerity demonstration outside parliament in Athens turned violent.
Last night's clashes came as Greek politicians began debating contentious measures needed to start negotiations on a new bailout and avoid financial collapse.
Groups of youths among the more than 12,000 protesters smashed shopfronts and set at least one vehicle alight. It was the first significant protest violence since the left-wing Syriza government came to power in January promising to repeal bailout austerity.
Police said at least 50 people were arrested. The protest was timed to coincide with the start of debate on the Bill, which includes consumer tax increases and pension reforms that will condemn Greeks to years of more economic hardship.
The Bill has fuelled anger among the governing left-wing Syriza party and led to a revolt by many party members against Prime Minister Alexis Tsipras, who has insisted the deal forged early on Monday after a marathon weekend eurozone summit was the best he could do to prevent Greece from crashing out of Europe's joint currency.
"I must tell you that Monday morning at 9.30, it was the most difficult day of my life. It was a decision that will weigh on me for the rest of my life," said Finance Minister Euclid Tsakalotos.
"I don't know if we did the right thing. But I know we did something with the sense that we had no choice. Nothing was certain and nothing is," he said as the debate kicked off.
Civil servants protested with a 24-hour strike that disrupted public transport and shut down state-run services across the country. Large numbers of Syriza politicians are almost certain to vote against the package.
Alternate Finance Minister Nadia Valavani resigned from her post, saying she could not vote in favour of the Bill.
In a letter sent to Mr Tsipras on Monday and released by the finance ministry today, Ms Valavani said she believed "dominant circles in Germany" were intent on "the full humiliation of the government and the country".
The economy ministry's secretary-general, Manos Manousakis, also resigned over the agreement.
Mr Tsipras agreed to a deal after a marathon 17-hour eurozone summit which ended on Monday morning. It calls for Greece to pass new austerity measures his government had battled against in return for the start of negotiations on a third bailout.