Smoke from petrol bombs spread across streets in Athens. Gangs of young people hurled stones and bottles and were chased by riot police firing tear gas through Syntagma square in front of the Greek parliament.
Helicopters buzzed overhead as violence flared during an anti-austerity march in the capital.
Reports indicate there have been no serious injuries with some 120 people detained.
Some of the rioters smashed bus stop kiosks and set fire to rubbish bins.
Authorities deployed twice as many police as those on duty at previous rallies in a bid to avoid a repeat of rioting which has flared at similar demos.
This was the single biggest demonstration since Greece’s coalition government took power in June and it paralysed the streets of Athens with the number of protesters estimated to be in the region of 70,000.
The march organised by the two largest trade unions was part of a 24-hour strike across the country.
It was called in protest at the latest round of planned spending cuts. The government must save 11.5bn euros as a precondition to receiving its next tranche of bailout funds.