Greek air traffic controllers are striking today as part of nationwide industrial action by the country's general employee union.
The walkout began at 00:01 local time and is to stop just before midnight today.
Flights across the country through Hellas upper information region (UIR) and Athinai flight information region (FIR) will not be affected, according to the Greek Air Traffic Controllers' Association (GATCA).
However, commercial flights to and from the country have been cancelled.
British Airways has suspended its flights to Athens today while EasyJet has cancelled most of its services between Greece and its European bases. A limited number of flights by the UK-headquartered budget carrier have been transferred to 6 October.
Military flights by the Hellenic Air Force as well as emergency, search-and-rescue and head of state flights are taking place today.