The violent protesters, usually identified as self-styled anarchists and anti-state activists, threw stones and homemade firebombs against police, who responded with the use of teargas. Scenes of widespread vandalism in and around Syntagma Square were again shown live on local and international television.
Just before 2 p.m. local time, police barricades in front of the Monument of the Unknown Soldier outside Parliament were overturned by protesters, prompting extensive use of teargas by anti-riot police.
In spite of the clashes, hundreds of people from the "indignados movement" remained at Syntagma Square, continuing peaceful demonstrations against the austerity measures, even in the face of provocations by the violent self-styled anarchists.
Since early this morning, downtown Athens is off limits for vehicles.
Sixteen people were injured in the clashes and taken to a nearby hospital. Only one person remained hospitalised. Police said 30 of its officers were injured.
Later in the afternoon, authorities said 18 individuals were arrested and led before a prosecutor, six of which were later charged with felony counts. The rest were slapped with misdemeanour charges.
Earlier, individuals participating in the "indignados movement" engaged in a brief verbal altercation with members of the communist party-affiliated PAME trade union, which had organised a separate protest rally.
ND party attacks gov't over violence in central Athens
The main opposition New Democracy (ND) party on Wednesday vigorously condemned the violent incidents outside the Greek Parliament, which occurred during demonstrations, accusing the government and particularly the citizen's protection ministry of "resorting to an inconsiderate use of tear gas."
"A small group of hooded people have succeeded in disrupting Athens's historical centre. Hotels are evacuated, the metro station has been turned into a gas chamber, innocent peaceful demonstrators have been trapped, while ambulances are not able to take injured citizens," party spokesman Yiannis Michelakis said.
The political leadership of the Citizen's Protection Ministry showed that it had no plan at all against the self-styled anarchists, he said, charging that "it resorts to the inconsiderate use of tear gas, which has transformed the capital's centre into hell."
The responsibilities Citizen's Protection Minister Christos Papoutsis "are self-evident and great," Michelakis concluded.