At least five people have been arrested after police clashed with demonstrators protesting against compulsory vaccination in central Athens.
Police fired tear gas, stun grenades and water canon to disperse the crowds from Syntagma Square, in front of the parliament building.
An estimated 3,500 people took part in the protests.
Some protesters wore religious garb while others carried icons and Greek flags. Leaflets from far-right parties were also distributed at the protests.
According to the police, the trouble started when protesters were requested to clear Amalias Avenue, where they were obstructing traffic.
When protestors started throwing bottles and other objects at the police, the police responded with water canon and tear gas.
Outside the University of Athens, there were clashes between anti-authoritarians and anti-vaccination protestors.
Meanwhile in Thessaloniki, citizens, responding to an call put out on the internet, held a rally and march against compulsory vaccination.
The demonstrators gathered in the White Tower and then marched through the main streets of the city, holding banners, Greek flags, crosses and icons and shouting slogans against the government and mandatory vaccination.
These protests come after the Greek Health Ministry submitted an amendment to Parliament on Wednesday according to which healthcare professionals will remain on unpaid leave if they do not get vaccinated against COVID-19.
Infections in Greece have been rising in recent weeks, and authorities reported almost 3,000 new cases on Wednesday, bringing the total since the pandemic began to 463,473 people. More than 12,800 have died.