|Police fired tear gas at a group of hooded youths, who had thrown petrol bombs, rocks and sticks [AFP]
Thousands of people have taken to the streets of Athens, the Greek capital, as unions began a 24-hour nation-wide walkout in protest against the government's austerity measures.
A group of hooded youths threw petrol bombs, rocks and sticks at police, who responded with tear gas, as around 15,000 people marched to parliament.
At least seven people were injured, reports said, and police said they had detained five people for questioning.
Public services including trains, ferries and flights have been disrupted or halted by the strike, which began on Wednesday morning.
The action comes as the Greek government seeks new terms for its $158bn joint European Union-International Monetary Fund bailout, and reports that the country may need additional support.
The government has already brought in a range of tough spending cuts to comply with the bailout, but the unpopular measures have led to massive protests over the past year.
This month, the government is planning to pass further measures aimed at saving an estimated $33bn through 2015.
"We strongly protest against the unfair and harsh policies that have pushed up unemployment, widen false employment and trample on worker rights," GSEE, the leading Greek union, said as the strike began.
In Athens' port of Piraeus striking ferry electrician Athanassios Sidiropoulos said the government was trying to scrap rights won over the course of decades by working classes.
"All seamen should have pension and healthcare rights, collective labour contracts, healthcare contributions,'' he told the AP news agency.
Around 3,000 members of the Communist-led PAME union marched through the streets of Athens, and separate street protests by other unions are scheduled later in the day.
Some banks were shut but others remained open for business, their fronts protected by rolled down shutters in anticipation of the demonstrations.
Greece's overall debt has exploded to $490bn, leading to mounting speculation, including among some Greek officials, that it will need alternative options to keep up with repayments when the EU-IMF loan runs out in 2013.
Senior EU and Greek officials have denied that any debt restructuring is on the agenda, although eurozone officials have begun to admit that Greece is likely to need more aid in some form.
At the weekend, the head of the Eurogroup of eurozone finance ministers, Jean-Claude Juncker, said that "we think that Greece does need a further adjustment programme".
Eurozone ministers are due to debate the crisis next week but no decision will be taken immediately, a German official told the Reuters news agency on Wednesday.
European Union Economic Affairs Commissioner Olli Rehn, who is the top EU official behind bailout negotiations, has said a decision on further aid is a few weeks away, pending the result of the audit.