Thousands blocked the road outside Greek state broadcaster ERT headquarters just hours after riot police evicted journalists occupying the site.

There were reports that police had used tear gas to drive the 50 or so media workers out of the station during the pre-dawn raid.

Four people, including ERT union Pospert president Panagiotis Kalfayiannis, were arrested but released soon after.

Journalists had been occupying ERT headquarters since June 11, when the government unilaterally decided to shut down the public broadcaster and fire all 2,700 staff, prompting junior coalition partner Democratic Left to leave the government.

Staff continued to produce unofficial broadcasts - including news reports and documentaries - online and using the Communist Party's (KKE) stations.

Former regional ERT stations were have been carrying on with unauthorised programming and there was also a demonstration outside the ERT site in Thessaloniki.

Government spokesman Simos Kedikoglou said the eviction was to "restore the rule of law.

"The broadcasting complex had been illegally occupied, and that resulted in daily financial losses for the Greek state.

"The intervention was carried out in the presence of a prosecutor," he said.

But it prompted anger from trade unionists around the world.

British National Union of Journalists general secretary Michelle Stanistreet said: "This is an attack on press freedom, workers and their trade unions. We stand opposed to the shutdown of Greece's national public broadcaster and stand in support with our colleagues."

And the International Federation of Journalists (IFJ) expressed its "shock and anger at this absolutely unnecessary action ... in what is supposed to be a democratic country."

IFJ president Jim Boumelha called on Greek authorities to leave the building immediately and "return it to ERT media workers and journalists."

The KKE denounced the clear-out, arguing that it proved "the unpopular, anti-worker policy goes hand-in-hand with the intensity of authoritarianism and repression."

Main opposition party Syriza filed a motion of censure in Parliament after the raid.

"You have no social support and popular legalisation," said party leader Alexis Tsipras.

"The destructive course has to stop now."