Athens: About 30,000 people protested in Athens' central Syntagma square on Sunday evening against the government's tough economic austerity policies.

The demonstration, larger than many others that have taken place during Greece's economic crisis, appeared to be the first that resulted from spontaneous calls over social media sites. Many others have been organised by unions or political factions.

Pointing at Parliament and its 300 legislators, many protesters chanted "Thieves! Thieves!" Others shouted slogans against Prime Minister George Papandreou and the International Monetary Fund.

No violence was reported and few police officers were on the scene.

Papandreou, buffeted by negative polls and protests such as these, has vowed to continue his fiscal reforms. On Sunday, he warned against "sirens" calling for Greece to default on its debt.

Speaking to an audience of local officials in western Greece, Papandreou said it is "foreign taxpayers' money" that has allowed his nation to continue paying public sector salaries and pensions.

Reforms are painful, but they are starting to pay off and the economy will return to growth in 2012, he said.