Public sector workers in Greece have launched a nationwide strike in protest at government measures to tackle the country's huge budget deficit.Flights have been grounded, many schools closed, and hospitals are operating an emergency-only service.
The government wants to cut pay, reduce pensions and revise the tax system.
EU leaders will discuss the issue during a summit in Brussels on Thursday amid concern the Greek crisis could threaten the credibility of the euro.
Financial markets around the world and politicians from across Europe will be watching the situation carefully, says the BBC's Jonny Dymond, in Athens.
Greek Prime Minister George Papandreou has already faced down a three-week protest by farmers demanding higher government subsidies.
Public anger
On Tuesday, his socialist government announced that it intends to raise the average retirement age in a bid to save the cash-strapped pensions system.
The move comes on top of other planned austerity measures, including a public sector salary freeze and a hike in petrol prices announced last week.
Public sector workers will not be hit as hard as they have been in Ireland, but they complain that some of the lowest paid will suffer while the rich dodge tax with impunity, our correspondent says.
Further government measures include the non-replacement of departing civil servants, and tax collectors recovering billions of euros lost to tax evasion.
Biggest threat
Greece's deficit is, at 12.7%, more than four times higher than eurozone rules allow. Its debt is about 300bn euros ($419bn; £259bn).
The markets remain sceptical that Greece will be able to pay its debts and many investors believe the country will have to be bailed out.
The uncertainty has recently buffeted the euro and the problems have extended to Spain and Portugal, which are also struggling with their deficits.
The possibility of Greece or one of the other stricken countries being unable to pay its debts - and either needing an EU bailout or having to abandon the euro - has been called the biggest threat yet to the single currency.
