Some people were caught up in the protests as they shopped
It is part of an industrial action organised by the civil service trade union, ADEDY.
On Wednesday, protesters hung huge banners on the Acropolis, the ancient site that dominates Athens, calling for "resistance".
Conservative Prime Minister Costas Karamanlis has rejected calls to step down, despite growing public pressure.
But earlier this week he acknowledged some of the problems that had fuelled the anger of young people.In a speech to parliamentary colleagues on Tuesday, he said "long-unresolved problems, such as the lack of meritocracy, corruption in everyday life and a sense of social injustice disappoint young people"
The New School in Exile