Greece's lawmakers approved a key austerity bill on Wednesday, paving the way for the country to get its next vital bailout loans that will prevent it from defaulting on its debts next month.

The unpopular 28-billion-euro ($40 billion) five-year package of spending cuts and tax hikes was backed by a majority of the 300-member parliament on Wednesday, including Socialist deputy Alexandros Athanassiadis, who had previously vowed to vote against. A conservative deputy who broke ranks with her party's line also voted in favor, bolstering the government's majority of five seats in the 300-member parliament.

Another bill detailing measures to implement the measures goes for a vote on Thursday.

The European Union and International Monetary Fund have demanded both bills pass before they approve the release of a 12-billion-euro loan installment from last year's rescue package.

Greece has been relying on 110 billion euros ($157 billion) in bailout loans for the past year, and without the next installment it faces becoming the first eurozone country to default next month.

The vote took place as clashes between police and protesters broke out outside parliament, with the booms of stun grenades and tear gas resonating across the square outside the building.

In the run-up to the vote, violence engulfed the square outside. Riot police fired volleys of tear gas at swarms of young men who were hurling rocks and other debris as well as setting fire to trash containers.

Police with truncheons occasionally charged the demonstrators, but pulled back just as quickly.

Police stun grenades boomed and flashed, often drawing jeers and boos from the crowds.

Most of the anti-government protesters who marched to the square stayed clear of the fighting, but they vented their anger at the political establishment with chants and insults.

The vote comes against a backdrop of violent demonstrations and on the second day of a nationwide general strike that has brought much of Greece to a standstill. Hundreds of flights and ferries have been canceled, leaving tourists stranded during the summer high season.

Protesters were trying to encircle parliament to prevent deputies from entering and voting for the bill and a massive security operation was under way, with a large section of central Athens sealed off to traffic.

Scuffles broke out early in the morning as demonstrators attempted to block a major avenue leading to the center of the city, and to parliament. Riot police responded with pepper spray, and 10 people were treated in a nearby hospital for minor injuries, hospital officials said.

Demonstrators also hoisted ghoulish effigies of men they hold responsible for Greece's misfortune - Papandreou, new Finance Minister Evangelos Venizelos and Deputy Prime Minister Theodoros Pangalos - and shook them in the air on sticks.

"Dogs, you look after your masters," they chanted at police. The furious marchers also emptied bags of garbage from municipal containers and lobbed them at the security forces, who stood their ground impassively.

A day earlier, extensive clashes left at least 46 people injured, most of them police, as rioters pelted police with chunks of marble and ripped up paving stones, and authorities responded with repeated volleys of tear gas and stun grenades.

Greece has said it has funds only until mid-July, after which it will be unable to pay salaries and pensions, or service its debts, without the next bailout installment from the eurozone and the International Monetary Fund.