Greek police have fired teargas at protesters throwing stones and petrol bombs in Athens, as at least 50,000 striking workers marched to parliament in the country's biggest anti-austerity rally in months.

Flights and trains were suspended, shops pulled down their shutters and tens of thousands took to the streets on Wednesday.

In Athens, more than 50,000 people chanted: "We won't submit to the troika (of lenders)" and "EU, IMF Out!".

The rally marched past Athens' central Syntagma square to parliament to protest against a new round of belt-tightening demanded by EU and IMF lenders as the price for fresh aid.

"We can't take it anymore - we are bleeding. We can't raise our children like this," said Dina Kokou, a 54-year-old teacher and mother of four who lives on 1,000 euros a month.

"These tax hikes and wage cuts are killing us."

The strike, called by the country's two biggest unions representing half the four-million-strong work force, is shaping up to be the first test of whether Prime Minister Antonis Samaras can stand his ground in the face of popular protests.