Greek police fired tear gas at the demonstrators, and the protesters threw rocks in retaliation. No casualties were visible.
The protesters gathered in Syntagma Square outside the Greek Parliament building in the center of the capital, where lawmakers will vote Wednesday on an austerity package of tax increases and spending cuts.
Watch a live stream of the protests below:
Police in riot gear set up barricades outside the Parliament building. Most of Greece’s transportation systems were halted, and hospitals were barely opened. Government offices, schools, and courts have closed.
But thousands of marchers still gathered, with members of the communist PAME labor union waving signs that read “No sacrifices for plutocracy,” and chanting, “Workers, you can live without a boss.”
Two larger unions launched their efforts around noon.
The Greek defense minister, Panos Beglitis, has warned of a “catastrophe” if Parliament does not approve the austerity package. Greece must pass the package if it is to receive bailout funds from the E.U. and IMF and stave off a possible default.
Greeks and journalists tweeted updates from the Syntagma Square, using the hashtag #Syntagma
One journalist tweeted: “This protest ended the way all protests end -- street fights btn police + anarcho-leftists. Yet portrayed as mass Athens riot.”
More photos of the protests below: