In Athens, masked youths threw firebombs at police outside parliament.
Police responded with tear gas and stun grenades, temporarily halting the demonstration of around 30,000 people. No injuries or arrests have been reported.
Greeks rallied to mark the 38th anniversary of the day in 1973 when military tanks quashed a student rebellion at the Athens Polytechnic.
Some 7,000 police officers were deployed as the city braced itself for anti-austerity demonstrations arising from the annual march.