Authorities have declared a state of emergency on a second Greek island as a series of earthquakes continued to rattle the south-eastern Aegean Sea region.

The emergency measure announced on the island of Amorgos follows a similar decision for nearby Santorini on February 7 after thousands of unusual tremors were registered in an undersea area

Experts say the Greek island of Santorini has been hit by more than 1,000 earthquakes, but they're not linked to the region's active volcanoes.