An 5.6-magnitude earthquake struck just off the Greek island of Crete in the early hours of Monday morning, according to the Athens Observatory, but there were no immediate reports of casualties or damage.
The epicentre of the quake, described as "very powerful", was in the Mediterranean Sea, some 430 kilometres (267 miles) to the southeast of Athens, the Observatory said.
The quake, recorded at 12:39 am local time (2239 GMT), followed a 6.2-magnitude earthquake that struck on Saturday off the southern coast of Crete.
Other smaller aftershocks have also affected the island, popular with holidaymakers.
Greece is the European country that is most frequently hit with earthquakes.