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.

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.

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 series of earthquakes near the Greek island of Santorini have led authorities to shut down schools, dispatch rescue teams with sniffer dogs and sent instructions to residents including a request to

Schools on the Greek island of Santorini have been told to close on Monday in response to an increase in seismic activity in recent days. Authorities have also advised against "large gatherings in enclosed spaces" across the island - a popular tourist destination known for its whitewashed buildings and blue domed churches.

Fresh overnight tremors shook Greece's top tourist island Santorini, media reports said Monday, prompting people to sleep outdoors and others to leave by plane or ferry.