ATHENS (Reuters) -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.

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.

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 officials are warning those on the popular tourist island destination of Santorini to stay alert in the coming days due to increasing seismic activity which could mean a strong earthquake is possible.