The strong quake struck 82 kilometres (51 miles) northeast of Crete's capital Heraklion at 0319 GMT at a depth of 68 kilometres (42 miles), the USGS said.
State television ERT said many residents in the Cretan regions of Rethymno and Lasithi were woken by the quake just after 6:00 am and quickly exited their homes as a precaution.
State news agency ANA said fire department units in Crete had been placed on general alert, with vehicles patrolling to assess the situation.
The quake struck just over a week after a 6.1-magnitude tremor hit near the island of Kasos near Crete, and was felt in the outlying area.
Thousands of earthquakes, mainly of low magnitude, have been recorded since January between the islands of Santorini, Amorgos, Ios and Anafi in the Cyclades group southeast of the Greek mainland.
Located where the African and Anatolian tectonic plates converge, the Aegean Sea is often hit by quakes.
But the region had not experienced a phenomenon of such magnitude since records began in 1964, experts say.
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