Schools were closed and emergency crews deployed on the volcanic Greek island of Santorini on Monday after a spike in seismic activity raised concerns about a potentially powerful earthquake.Precautions were also ordered on several nearby Aegean Sea islands — all popular summer vacation destinations — after more than 200 undersea earthquakes were recorded in the area over the past three days.

Schools have been shut and public gatherings are being discouraged on the Greek island of Santorini as local authorities put the popular tourist spot on high alert for a big earthquake, following scores of small temblors over the last two days.

Prominent Greek seismologist Gerasimos Papadopoulos cautioned that the current earthquake sequence – displayed on live seismic maps as a growing cluster of dots between the islands of Santorini, Ios, Amorgos, and Anafi — could indicate a larger impending event.