Greek unions Friday unleashed a 48-hour strike against new austerity measures to go before parliament and required by the European Union and the IMF in exchange for badly needed aid.
The measures, dubbed "the grave of Greek society," sparked a strike call by the CSEE and Adedy unions that together claim more than a million members.
The Greek population totals a little more than 10.7 million.
Protestors were called again to Syntagma Square, the scene of often violent demonstrations against austerity measures over the past two years.
The Greek capital was deprived Friday of bus, metro and trolley services, and security forces took up positions in the centre of the capital, where a rally began around 0930 GMT.
On Tuesday more than 20,000 people demonstrated in Athens and Greece's second city Thessaloniki during the first general strike of the year.
Greece's three-party coalition agreed Thursday to a new wave of labour-related cuts to pave the way for a 130 billion euro eurozone bailout before a loan repayment on March 20 which Athens cannot meet without assistance.
According to reports and party leaks, the measures include a 22 percent cut in the minimum wage, a 15 percent cut in complementary pensions and 15,000 civil service redundancies to meet a target of 150,000 layoffs by 2015.