The offshore quake hit at a depth of 74 kilometres (45 miles), about 23 kilometres from the island's capital of Fry around 1:50 am (22:50 GMT Tuesday).

The USGS had initially estimated a 6.1-magnitude quake slightly closer to Fry.

Shaking was felt across the region, including as far away as Cairo, but Egypt's National Research Institute of Astronomy and Geophysics reported no damage and no aftershocks detected.

Greece is located on a number of fault lines, and is sporadically hit by earthquakes.

Between January 26 and February 13, more than 18,400 quakes, mainly of a low magnitude, were recorded off islands in the Cyclades archipelago, according to the University of Athens (EKPA) seismology laboratory.

The seismic swarm caused no casualties or significant damage, but worried authorities and residents.