ATHENS, Greece (AP) _ Hundreds of youths have smashed and looted stores in central Athens and clashed with riot police during a massive anti-government rally against painful new austerity measures that won initial parliamentary approval in a vote.

Wednesday's rioting came on the first day of a 48-hour nationwide general strike that brought services in much of Greece to a standstill, grounding flights for hours, leaving ferries tied up in port and shutting down customs offices, stores and banks.

More than 100,000 people took to the streets of the Greek capital to demonstrate against the austerity bill, which includes new tax hikes, further pension and salary cuts, the suspension on reduced pay of 30,000 public servants and the suspension of collective labor contracts.

Creditors have demanded the measures before they give Greece more funds from a (euro) 110 billion ($152.11 billion) package of bailout loans from other eurozone countries and the International Monetary Fund. Greece says it will run out of money in mid-November without the (euro) 8 billion ($11 billion) installment.

But Greek citizens said they already are reeling from more than one-and-a-half years of austerity measures.

``We just can't take it any more. There is desperation, anger and bitterness,'' said Nikos Anastasopoulos, head of a workers' union for an Athens municipality, as he joined the demonstration early in the day.

The bill won initial approval in the 300-member Parliament late Wednesday, with 154 deputies voting in favor on principle and 141 against. A second vote, on the bill's articles, is due Thursday. Only after that procedure will the bill have passed. A communist party-backed union has vowed to encircle Parliament Thursday in an attempt to prevent deputies from entering the building for the procedure.

The new measures have even prompted some lawmakers from the governing Socialists to threaten not vote for at least some of the articles in the bill. But Finance Minister Evangelos Venizelos insisted there was no choice but to accept the hardship.

``We have to explain to all these indignant people who see their lives changing that what the country is experiencing is not the worst stage of the crisis,'' he said in Parliament. ``It is an anguished and necessary effort to avoid the ultimate, deepest and harshest level of the crisis. The difference between a difficult situation and a catastrophe is immense.''

Hours before Wednesday's vote, one of Athens' largest demonstrations in years degenerated into violence as masked and hooded youths pelted riot police outside Parliament with gasoline bombs and chunks of marble smashed from buildings, metro stops and sidewalks.

Police responded with tear gas and stun grenades. Authorities said 50 police were injured in the clashes, along with at least three demonstrators, while 33 people were detained for questioning or arrested for alleged involvement in the rioting. At least three journalists covering the riots were also slightly hurt.

Long after Wednesday's demonstration was over, violence continued, with police fighting running street battles with youths setting up burning barricades along the back streets near Athens' main Syntagma Square and near the tourist area of Monastiraki.

Thick black smoke billowed from burning trash and bus-stops, and debris lay strewn along the capital's broad avenues. A hurled gasoline bomb set fire to a sentry post used by the ceremonial presidential guard at the Tomb of the Unknown Soldier outside Parliament.

In Greece's second city of Thessaloniki, protesters smashed the facades of about 10 shops that defied the strike and remained open, as well as five banks and cash machines. Police fired tear gas and threw stun grenades.

The general strike is set to continue Thursday, with all sectors _ from dentists, hospital doctors and lawyers to tax office workers, taxi drivers, prison guards, teachers and dock workers _ staying off the job.

Air traffic controllers scaled back their strike from 48 hours to 12, allowing flights to take off and land after noon on Wednesday.

Meanwhile, European countries are trying to work out a broad solution to the continent's deepening debt crisis, before a weekend summit in Brussels. It became clear earlier this year that the initial bailout for Greece was not working as well as had been hoped, and European leaders agreed on a second, (euro) 109 billion ($151 billion) bailout. But key details of that rescue fund, including the participation of the private sector, remain to be worked out.