Hundreds of youths pelted riot police with fire bombs, bottles and chunks of marble today as another Greek anti-austerity demonstration descended into violence, less than a month after more intense clashes broke out during a similar protest.

Authorities said around 70,000 protesters took to the street in two separate demonstrations in Athens during the country's second general strike in a month as workers across the country walked off the job to protest against new austerity measures the government is negotiating with Greece's international creditors.

The strike was timed to coincide with a European Union summit in Brussels later in the day, at which Greece's economic fate will is likely to feature large.

Riot police responded with volleys of tear gas and stun grenades in the capital's Syntagma Square outside Parliament as protesters scattered during the clashes, which continued on and off for about an hour. Another general strike in late September had also seen limited, but much more intense, clashes between protesters and police.

A 65-year-old protester suffered a fatal heart attack during the demonstration but efforts to revive him failed. The organisers of the protest march he participated in said the man had fallen ill before any rioting had broken out.

Four demonstrators were injured after being hit by police, volunteer paramedics said. The Health Ministry said two of the protesters were treated in hospital and that their injuries were not serious. Three policemen also required hospital treatment.

Hundreds of police had been deployed in the Greek capital ahead of the demonstration. Police said seven people were arrested today, out of more than 100 detained.

The strike grounded flights, shut down public services, closed schools, hospitals and shops and hampered public transport in the capital. Taxi drivers joined in for nine hours, while a three-hour work stoppage by air traffic controllers led to flight cancellations. Islands were left cut off as ferries stayed in ports.

Athens has seen hundreds of anti-austerity protests over the past three years, since Greece revealed it had been misreporting its public finance figures.

The country has been surviving since then with the help of two massive international bailouts. To secure them, it has committed to drastic spending cuts, tax hikes and reforms, all with the aim of getting the state coffers back under some sort of control.

But while significantly reducing the country's annual borrowing, the measures have made the recession worse. By the end of next year, the Greek economy is expected to be around three quarters of the size it was in 2008. And with one in four workers out of a job, Greece has, along with Spain, the highest unemployment rate in the 27-nation European Union.

"We are sinking in a swamp of recession and it's getting worse," said Dimitris Asimakopoulos, head of the GSEVEE small business and industry association. "180,000 businesses are on the brink and 70,000 of them are expected to close in the next few months."

The country's four-month-old coalition government is negotiating a new austerity package with debt inspectors from the EU, International Monetary Fund and European Central Bank.