Dozens of masked youths are clashing with police at a union protest in Athens during a general strike against the cash-strapped government's planned pension and labor reforms.

Riot police fired tear gas and stun grenades to disperse troublemakers who threw chunks of marble smashed off a metro station entrance and set rubbish bins on fire.

No injuries, arrests or major damage to property were immediately reported

Tuesday's violence came as some 10,000 people took part in a demonstration organized by the country's two main labor unions and fringe left-wing groups. A separate march by some 5,000-6,000 members of the Communist Party-backed PAME union ended peacefully.

The strike disrupted public transport and left hospitals operating on emergency staff.