Riot police have used tear gas and stun grenades on youths throwing petrol bombs during a huge march protest march through Athens over government cuts.
The clashes came during a 24-hour general strike that brought most public services to a halt, suspended all train and ferry services, grounded flights for four hours and disrupted public transport.
Dozens of black-clad anarchists smashed bus stops, set rubbish bins on fire and broke shop windows.
The fighting divided the 40,000 strong march - which was otherwise peaceful - into two.
At one stage, choking clouds of chemicals fired by police sent demonstrators and tourists scurrying for cover past shops and banks that had their fronts shuttered in anticipation of trouble.
Several thousand people - some chanting "Finance Minister, leave the planet" - took part in the demonstration called by the two main labour unions. Previous protests have also been marred by violence, and three clerks died last May when their bank was torched by rioters.
Earlier about 10,000 members of the Communist-led PAME union held a peaceful protest, with banners reading "We reject and condemn the new measures. We're intensifying the fight."
Another 8,000 people joined in two separate protests in the northern city of Thessaloniki.
Greece's crisis follows years of inept government, widespread corruption and waste that created bloated budget deficits and a public debt considerably larger than annual economic output.
For the time being, the country is shielded from insolvency by a package of EU and IMF rescue loans.