Masked demonstrators hurled firebombs at police and broke car and shop windows yesterday as thousands of secondary school students and their supporters marched through Athens in protest against education reform.
Large demonstrations also took place in Thessaloniki and several other cities throughout Greece.
Television showed a homemade bomb bursting in front of a police officer in central Syndagma Square, briefly setting him alight. He was taken to hospital.
Students were also seen fighting among themselves while stones and oranges were hurled sporadically at shop and car windows.
Riot police attempted to keep the masked protesters, who often create violence on the edges of Greek demonstrations, away from the main body of marchers.
The Education Minister, Mr Gerassimos Arsenis, whose proposed reforms have brought about months of protests and school occupations, was burnt in effigy, as was an EU flag.
Thousands of students, most in their mid- to late teens, swarmed through Athens protesting against the government education plans that include a new evaluation system and university exams they believe will make it harder for them to get higher education.
They banged drums, chanted and carried banners saying "We Will Win" and "You Cannot Stop Us".
The demonstrators were supported by many teachers, who also face new testing requirements and forced overtime, and a number of parents.
"I support the children's protest. The law will take away the few rest hours that they have and won't give them any knowledge in return," said Mrs Maria Niko foridis, a mother of two demonstrators.
Students across the country have occupied schools and set up temporary road blocks since last autumn.
The number of schools being occupied has dropped since the Christmas holidays, but Greek newspapers reported yesterday that some 600 of the country's 3,000 high schools were still under student occupation.
The continuing strife has had political repercussions, putting Mr Arsenis under pressure to resign. The opposition New Democracy party began a debate on a motion of no confidence against him on Thursday. It is expected to fail when it comes to a vote today.