Greek authorities have warned of an increase in seismic activity around the Aegean tourist island of Santorini, advising people to avoid four ports, empty their pools, refrain from gathering in indoor spaces and shut schools on Monday.

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.

Increased volcanic activity in Greece’s famed tourist hotspot of Santorini has prompted the country’s civil protection minister to call a meeting with local and disaster response officials.