Riot police in Athens have clashed with anti-austerity protesters who hurled stones and petrol bombs on another day of general strikes that brought much of Greece to a standstill.

Almost 40,000 demonstrators took to the streets in Athens during the 20th national strike in Greece since the euro crisis began.

Riot police fired tear gas at protesters who threw projectiles and Molotov cocktails.

A 65-year-old man died from a heart attack not far from the clashes, while another three people were injured.

Police detained about 50 protesters.

Most business and public sector activity ground to a halt at the start of the 24-hour strike, which was called by the country's two biggest labour unions, ADEDY and GSEE.

"Enough is enough. They've dug our graves, shoved us in and we are waiting for the priest to read the last words," said Konstantinos Balomenos, a 58-year-old worker at a water utility whose wage has been halved to 900 euros and who has two unemployed sons.

It was the third time since late September that tens of thousands of Greeks have taken to the streets, holding banners and chanting slogans to show their anger at austerity policies imposed by EU and IMF lenders in exchange for aid.

Some were carrying Greek, Spanish and Portuguese flags and shouted: "EU, IMF out".

"Agreeing to catastrophic measures means driving society to despair and the consequences as well as the protests will then be indefinite," said Yannis Panagopoulos, head of the GSEE private sector union, one of two major unions that represent about 2 million people, or half of Greece's workforce.

Greece is stuck in its worst downturn since World War II and must make at least 11.5 billion euros of cuts to satisfy the "troika" of the European Commission, European Central Bank and IMF, and secure the next tranche of a 130-billion-euro bailout.

European Union leaders will try to bridge their differences over plans for a banking union at a two-day summit which starts on Thursday.

No substantial decisions are expected at the summit, reviving concerns about complacency in tackling the debt crisis which exploded three years ago in Greece.