Protesters clash with riot police in Athens.

Protesters clash with riot police in Athens. Photo: Getty Images

ATHENS: Greek riot police have fired tear gas at protesters on the sidelines of a large anti-austerity rally in Athens during a national general strike as EU leaders prepared to tackle the eurozone crisis at a summit in Brussels.

As brief clashes broke out, officials said a 65-year-old protester collapsed and died from a heart attack but it was not immediately clear if his death was linked to the sporadic bursts of tear gas.

One in four people is officially unemployed. 

"A 65-year-old man was taken to hospital where efforts to revive him failed," a health ministry source told AFP, adding: "There were no bruises on his body."

A fireboomb explodes in front of riot police during clashes with demonstrators.

A fireboomb explodes in front of riot police during clashes with demonstrators. Photo: AFP

A police source said the man was picked up several hundred metres from the area where the clashes took place, while other reports said he was found on central Syntagma Square, close to the scene.

The ministry official said three people had also been injured in the clashes that broke out around Syntagma Square during the protest against a new wave of austerity cuts that the government is preparing to introduce next month.

Tens of thousands of people took part in the Athens protest, while a smaller demonstration was held in Greece's second city Thessaloniki, ahead of a broader mobilisation in southern European countries planned for next month.

Anti-austerity ... protesters gather in Athens as a general strike brought the city to a halt.

Anti-austerity ... protesters gather in Athens as a general strike brought the city to a halt. Photo: AFP

The police said some 26,000 people joined rallies in Athens but reporters on the scene estimated the number to be much larger.

Scattered groups of youths threw stones and firebombs at the police, who retaliated with tear gas and stun grenades then charged to clear the square.

Greeks reject additional cutbacks the government plans next month in order to unlock access to EU-IMF loans.

One in four people is officially unemployed – the real number is higher still, unions say – and the economy is in its sixth year of recession.

The head of the leading GSEE union, Yiannis Panagopoulos, indicated that another general strike would be held in Greece on November 14, part of a European mobilisation by unions that would also hit Portugal and Spain.

The coalition government of the Prime Minister, Antonis Samaras, is holding delicate negotiations with Greece's so-called troika of creditors – the EU, IMF and European Central Bank – to secure the release of loans needed to avoid bankruptcy.

The government has been told by its creditors to jump-start flagging economic reforms and cut the budget by €9.2 billion ($11.7 billion) next year in order to secure a €31.5 billion loan slice next month.

Agence France-Presse