There were no immediate reports of damage or injuries.
The quake was also felt in the nearby Turkish provinces of Mugla, Izmir, and Antalya, with Turkey’s AFAD emergency management agency saying it had a preliminary magnitude of 5.4.
The undersea quake struck at 14:37 Greek time and had an epicentre nearly 400 kilometres southeast of Athens and 58 kilometres southeast of the Rhodes town of Lindos, the Athens Geodynamic Institute said.