Beating drums and chanting "Robbers, robbers!" more than 60,000 people incensed over hefty wage cuts and tax rises marched to parliament in the biggest protest for months over austerity policy required by international lenders.
In the capital, riot police fired a few rounds of teargas during minor scuffles with hooded youths hurling rocks and bottles during an otherwise peaceful demonstration.
The two biggest labor unions brought much of crisis-ridden Greece to a standstill during a 24-hour protest against policies which they say deepen the hardship of people struggling through the country's worst peacetime downturn.
Representing 2.5 million workers, the unions have gone on strike repeatedly since a debt crisis erupted in late 2009, testing the government's will to impose the painful conditions of an international bailout in the face of growing public anger.
"Today's strike is a new effort to get rid of the bailout deal and those who take advantage of the people and bring only misery," said Ilias Iliopoulos, secretary general of the ADEDY public sector union, which organized the walkout along with private sector union GSEE.
"A social explosion is very near," he told Reuters from a rally in a central Athens square as police helicopters clattered overhead.
The eight-month-old coalition of Prime Minister Antonis Samaras has been eager to show it will implement reforms promised to the European Union and International Monetary Fund, which have bailed Athens out twice with over 200 billion euros.
The government has cracked down on striking workers, invoking emergency laws twice this year to get seamen and subway workers back to work after week-long walkouts that paralyzed public transport in Athens and led to food shortages on islands.
Demonstrations were also under way in Greece's second-biggest city, Thessaloniki, and on the island of Crete where dozens of protesters hit the streets waving black flags.
Labor unrest has picked up in recent weeks. A visit by French President Francois Hollande in Athens on Tuesday went largely unreported because Greek journalists were on strike.
"The period of virtual euphoria is over," said opposition leader Alexis Tsipras, whose Syriza party has regained a narrow opinion poll lead over the governing conservatives.
"Those who thought Samaras would renegotiate the terms of the bailout ... are now faced with the harsh reality of unpaid bills, closed shops and lost jobs," he said.
(Writing by Karolina Tagaris; Editing by Mark Heinrich)