Greece’s parliament has passed a controversial package of austerity measures, demanded by the eurozone and IMF in return for a 130bn-euro ($170bn; £110bn) bailout to avoid default.
The vote came amid some of the worst violence seen in Greece in years.
Protesters outside parliament threw stones and petrol bombs, and police fired tear gas. Several people were injured and buildings were set on fire.
PM Lucas Papademos urged calm, saying violence had no place in a democracy.
Lawmakers have also approved a related deal to write off 100bn euros of Greek debt held by private banks.
Pasok, the largest party, and its coalition ally New Democracy – which have both backed the bill – account for more than 230 deputies out of a total of 300.
There is mounting public anger in Greece and a feeling that the impact on ordinary people is beyond the value of the bailout, our correspondent adds.
Some reports say as many as 80,000 people joined demonstrations in Athens, with another 20,000 protesting in Thessaloniki.
Violent protests also spread to other Greek town and cities, including the holiday islands of Corfu and Crete, according to Reuters.
Running battles with police were still continuing in parts of the capital late on Sunday.
Dozens of police officers and at least 37 protesters were injured, 23 suspected rioters were arrested and a further 25 detained, AP reports.
Protesters hurled flares and chunks of marble torn up from the square. Some had tried to break through a cordon of riot police around the parliament.
Several historic buildings, including cafes and cinemas, were in flames. Syntagma Square – in the heart of Athens – is cloaked in a hail of tear gas, our correspondent says.
Ioannis Simantiras, 34, said the protesters were boxed in by the police.
The austerity measures include:
- 15,000 public-sector job cuts
- liberalisation of labour laws
- lowering the minimum wage by 20% from 751 euros a month to 600 euros
- negotiating a debt write-off with banks.
Mr Papademos had earlier said Greece did not have the luxury of such protests in such difficult times.
“Vandalisms, violence and destruction have no place in a democratic country and won’t be tolerated,” he said in a speech in parliament before the vote.