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.

A 112 emergency alert was sent on Monday afternoon to those in Santorini, following the series of earthquakes that have occurred over the past few days. The alert informs residents and visitors of the risk of landslides due to ongoing seismic activity. As a precaution, authorities have decided to prohibit access to three areas.