The first tremor, a 5.2-magnitude, struck at 5.15pm (local time) east of the island of Crete and at a depth of nine kilometres, the Institute of Geodynamics reported in Athens. The earthquake was felt in Crete and the islands of Karpathos, Kassos, Rhodes and Santorini, according to local media.
An even larger tremor of 5.4 magnitude struck at 8:59 pm (1859 GMT) about 25 kilometres northwest of the first, at a depth of 6.3 kilometres, the Institute of Geodynamics reported.
The mayor of the small island of Kassos, closest to the epicentre, told state news agency ANA that no buildings were damaged in either earthquake.
An unrelated 4.0-magnitude tremor also hit at 6:14 pm (local time) west of Athens, the Institute of Geodynamics reported. The epicentre was at a depth of 16.7 kilometres, it said.
Tremors of that magnitude are not uncommon in Greece, which lies close to a meeting point between the African and Eurasian tectonic plates. A second earthquake being stronger than the first is a rare occurrence, but it has happened on several occasions.