Greek police fired tear gas as protestors threw firebombs, burnt dustbins and vandalised shops on Wednesday at the start of a two-day strike ahead of a vote on a new austerity bill to stave off bankruptcy.
Police in Athens clashed with protesters outside parliament as more than 70,000 people according to authorities, and 200,000 according to unions, converged on central Syntagma Square.
At least 17 people including three civilians were injured, among them an off-duty officer struck by unknown assailants who seized his service handgun, a police source said. Nearly 5,000 policemen were on alert in the capital.
Tear gas blanketed central Athens as police fought to keep control on the square in front of the Greek parliament.
The violence began when some 200 youths hurled firebombs and pieces of masonry hacked off from neighbouring buildings at police from behind a steel barricade erected outside the parliament.
They vandalised shops, burnt dustbins and threw stones at the police.
A battle later broke out outside a row of luxury hotels on the square and a department store was vandalised as small groups of hooded and masked protesters broke away from the main demonstration.
The attackers also pelted police with broken masonry and smashed a police sentry box near the finance ministry.
Officers were also attacked in the city of Thessaloniki where the government's regional headquarters was assaulted by 100 protesters throwing firebombs.