The Istanbul-based Kandilli Observatory said the quake, with a preliminary magnitude of 6.2, occurred at 4:16 p.m. (1416 GMT) off the coast from Turkey's northwestern Canakkale province.
The earthquake was felt in the Turkish cities of Istanbul and Izmir, and their environs, officials said.
"It was one of the strongest earthquakes we have experienced," Mustafa Mutay, the mayor of the Turkish island of Bozcaada off Canakkale, told the state-run Anadolu Agency. "There was some panic during the quake, but things have returned to normal and there is no damage."
The Athens Geodynamic Institute in Greece put the magnitude at 5.8 and said the temblor occurred between the Greek islands of Lemnos and Lesvos, near the Turkish coast. The quake was mildly felt in Athens.
The U.S. Geological Survey gave a preliminary magnitude of 5.7.
Earthquakes are common in Turkey and Greece, both of which lie atop active fault lines.