Unions opposing austerity measures in Greece are staging their fourth general strike this year as the government prepares to start axing public sector jobs.
The walkout is disrupting flights, public transport, state hospitals and other services, while demonstrations are planned throughout the day.
The public sector has so far been spared from the job cuts that have hit the rest of the Greek economy since the country got its first international bailout in 2010.
However, the government has been forced to launch the cuts so it can continue receiving rescue loans from the International Monetary Fund and the other countries using the euro.
Parliament is set to vote on the new measures on Wednesday.