Greek authorities have declared a state of emergency on a second 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 near the two islands, as well as the islands of Ios and Anafi – all popular tourist destinations.

Scientists had expressed hope the seismic swarm could be easing up but a string of earthquakes around magnitude five has renewed concern.

Thousands have left the earthquake-struck island of Santorini (Petros Giannakouris/AP)

Seismologists have also noted that the epicentre of the earthquakes is steadily drifting northward in the direction of Amorgos.

The emergency declaration will facilitate rapid deployment of resources and emergency services.

The region has already seen a significant mobilisation of fire departments, police, coastguard and armed forces mostly on Santorini where thousands of residents and seasonal workers have left the island.

Overall, about 12,000 earthquakes with magnitudes greater than one have been registered since January 26, the University of Athens’ crisis management committee said earlier.

Although Greece lies in a highly seismically active part of the world and earthquakes are frequent, it is very rare for any part of the country to experience such an intense barrage of earthquakes for such an extended period.