Many of Greece's public services are in disarray because of a general strike in protest at the government's surprise move to shut down state broadcaster ERT with the loss of nearly 2,700 jobs.
The 24-hour strike, which includes Greek media, began at midnight (21:00 GMT).
Further protests and rallies are scheduled.
Prime Minister Antonis Samaras stands by his move, saying ERT is a "symbol of waste and lack of transparency".
The measure is designed to help Greece meet its debt bailout obligations.
The resulting general strike, which is the third this year, will affect tax offices, schools and hospitals.
It also means buses, trams and trains are not running, with no metro service to Athens' main airport.
ERT journalists are staging defiant sit-ins in the capital and in Greece's second city, Thessaloniki.
The government says riot police are stationed outside ERT offices to prevent "any destruction".
Most of the broadcaster's output has been taken off air since Tuesday, although shortwave radio and internet broadcasts continue.
'Coup'Journalists across all media are also calling for an indefinite protest - excluding those ERT stations airing rogue broadcasts maintained by workers who have refused to leave their posts.
Greek opposition leader Alexis Tsipras has described the closure as "illegal".
"Many times the word 'coup' is used as an exaggeration. In this case, it is not an exaggeration," he added.
But the country's conservative prime minister defended his decision.
"We are not closing down public radio and television. In fact, it is only now that we are going to get proper public radio and television," Mr Samaras said in a speech to business leaders on Wednesday night.
Corruption and mismanagement are widely known to exist within ERT, a public company symptomatic of Greece's past mistakes, the BBC's Mark Lowen in Athens reports.
But employees maintain successive governments were responsible as they were in charge, our correspondent adds.
The decision to close down ERT has also put strain on the country's governing coalition.
"We absolutely disagree with the government's particular decisions and management," the socialist Pasok party said in a statement.
The Democratic Left, another coalition partner, said restructuring ERT was necessary but should have taken place without shutting it.
The closure was also condemned by the head of the Orthodox Church of Greece, Archbishop Ieronymos, who said that ERT employees were being "sacrificed" to pay for decades of wasteful administration.
The Geneva-based European Broadcasting Union expressed "profound dismay" at the move.
The head of ERT's foreign desk, Odin Linardatou, said the announcement had taken journalists by surprise.
"We are very shocked, we are angry," she told the BBC's Newshour programme. "What I cannot accept in a democracy is that Greece will not have a public broadcaster."
The government says ERT was a huge drain on public resources, and will reopen at a later date under a new format and with considerably fewer staff.
All 2,655 employees will be compensated and allowed to apply for jobs at the revamped organisation.
The announcement came after months of strikes by ERT employees in opposition to plans to restructure the broadcaster.
Athens has pledged to cut thousands of public-sector jobs as part of agreements under which it receives billions of euros in rescue loans from the European Union and International Monetary Fund.
ERT, which began broadcasting in 1938, is funded by a direct payment of 4.30 euros (£3.80; $6) added monthly to electricity bills.
It ran three domestic TV channels, four national radio stations, as well regional radio stations and an external service, Voice of Greece.