According to the US Geological Survey the quake had a 6.4 magnitude, while the Athens Observatory, quoted by the state-run Athens News Agency, gave it a 6.2 magnitude.
The earthquake struck at 4:12 pm (1842 IST) in the sea some 60 kilometres off the city of Hania in western Crete, the agency said.
"The quake took place in an area known for its seismic activity. It was strongly felt in Crete but also in the rest of Greece," geology professor Efthymios Lekkas told Skai radio.
Greece is one of Europe's most earthquake-prone countries.
Yesterday, a 4.4-magnitude earthquake, described as "mild" by the observatory, struck the north of the country causing no damage.