"We have total participation," Stathis Anestis, a spokesman for GSEE, said.
"Workers want the policy to change. Those who created the crisis have to pay for it, not workers."
All boat links with the Greek islands were suspended, while rail traffic and urban transport was limited to services allowing strikers to reach rallying-points for demonstrations.
About 100 flights were cancelled by Greek airlines Olympic and Aegean as air-traffic controllers staged a four-hour walkout.
Media organistaions joined the strike, keeping news programmes off the air and preventing Friday's newspapers from being published.
About 20,000 people marched through the capital, Athens, in two separate protests organised by groups affiliated to the communist party.
"No compromise! Capitalism must pay for the crisis," protesters at one rally, organised by communist-backed groups, chanted.
"There is a problem in our society," Anna Hamosfagkidi, a lwayer, said.
"The situation is about to erupt and it concerns all of us, whether you've been fired or not. It is something that will knock on your door."
The conservative government of Costas Karamanlis, the prime minister, is struggling to cope with the global economic crisis and has fallen behind the opposition socialists in opinion polls.
Although the downturn has not yet hit hard in the form of bankruptcies and mass layoffs, Greece has scaled down its 2009 growth forecast to 1.1 per cent from 2.7 per cent.
The deficit is forecast to reach 3.7 per cent of gross domestic product in 2009.
The European Commission has told the government it needs to bring the deficit under three per cent by the end of 2010 and control spending to reduce overall debt, which at about 94 per cent of GDP is one of the highest in the bloc.