ATHENS, Greece (AP) — Multiple earthquakes are rattling Santorini, a volcanic island in Greece, prompting authorities to dispatch rescuers with tents, a sniffer dog and drones, and to shut schools on four islands.

Greece ’s top tourist island has been forced to shut its schools on Monday due to an increase in seismic activity in the area. Authorities have advised people on the Aegean island of Santorini to also avoid two small ports and refrain from gathering in indoor spaces after increased tremors in the area over recent days.

Schools were closed and emergency crews deployed on the volcanic Greek island of Santorini on Monday after a spike in seismic activity raised

The strongest earthquake recorded was magnitude 4.6 at 3:55 p.m. Sunday, at a depth of 14 kilometers (9 miles), the Athens Geodynamic Institute said.

Greek authorities have issued a warning to visitors to one of its most famous islands due to a surge in volcanic activity.