The Greek parliament has voted in favour of a drastic package of austerity measures intended to save the country from defaulting on its debts.
The proposed tax hikes and spending cuts have been deeply unpopular with the Greek public.
A nationwide 48-hour strike is under way and violent clashes are continuing in the streets of the capital, Athens.
The EU welcomed the bill's passage, by 155 votes to 138, as a "vote of national responsibility".
Greece is heavily in debt and the package is needed to win the latest tranche of a 110bn-euro (£98bn) loan from the EU and IMF.
Parliament will hold a second vote on Thursday aimed at reforming laws to allow the package to be implemented.
'No time to step back'
Ahead of Wednesday's vote, Prime Minister George Papandreou urged MPs to approve the package by consensus.
He had faced wavering support from within his governing Panhellenic Socialist Movement (Pasok), which has a slim majority, with 155 seats out of 300 in parliament.
But in the end, only one Pasok deputy voted against the package. There were two abstentions, while five deputies merely noted they were present.
Mr Papandreou says his austerity plan is the only way to get Greece back on its feet.
"We must avoid the country's collapse at all costs. Now is not the time to step back," he told deputies.
Were his 28bn-euro austerity package to be rejected, Greece could run out of money within weeks, as the EU and the International Monetary Fund want the measures implemented before they release more funds to help Greece pay off its vast debts.
European Commission President Jose Manuel Barroso and European Council President Herman Van Rompuy welcomed the result of Wednesday's vote, saying it had pulled Greece away from the "very grave scenario of default" while paving the way for a second aid package.
"The country has taken an important step forward along the necessary path of fiscal consolidation and growth-enhancing structural reform," they said in a joint statement.
'Unfair but necessary'
Once news that the vote had passed trickled out to the streets of Athens, fighting broke out with a new level of brutality, says the BBC's Malcolm Brabant in the Greek capital.
The riot police engaged in behaviour that would never be tolerated in other parts of Europe, throwing stones back at the protesters, says our correspondent.
Police corralled demonstrators into the metro station outside parliament in Syntagma Square, and fired tear gas down the stairwells, he adds.
Meanwhile, protesters set fire to a post office on the ground floor of the finance ministry in the square.
The air outside parliament was thick with plumes of tear gas and smoke as clashes continued near the square between masked protesters - armed with rocks and sticks - and riot police firing tear gas and stun grenades.
Dozens of police and protesters were injured in the violence.
"Let the prime minister come down here and see if he can live on 300 euros a month," one female protester told the BBC outside parliament.
Greek unions are angry that the government's austerity programme will impose taxes on those earning the minimum wage, following months of other cuts that have seen unemployment rise to more than 16%.
The vote covered the first part of Greece's austerity package, focusing on raising taxes to secure some 14.09bn euros over the next five years and introducing 14.32bn euros in public spending cuts.
Ahead of Wednesday's vote, the governor of Greece's central bank, George Provopoulos, said a 'no' vote would be "suicide" for the country.
Thursday's vote is over the implementation of different parts of the package, such as tax rises and the sale of state assets.
Once passed, European officials will start to finalise the details of a second bail-out, worth an estimated 120bn euros, designed to help Greece pay its debts until the end of 2014.
The impact of the Greek vote would be felt worldwide said Herman Van Rompuy, president of the EU Commission, on Tuesday.
Recently appointed Finance Minister Evangelos Venizelos acknowledged that the cuts were "unfair", though absolutely necessary.
But the main opposition leader, Antonis Samaras of the New Democracy party, said the thinking behind the austerity package was flawed, and that tax rates should be lowered rather than raised in order to stimulate the economy.