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.

Greek authorities have advised people on the Aegean island of Santorini to shut schools on Monday, avoid two small ports and refrain from gathering in indoor spaces after increased seismic activity in the area over recent days.

Greece's tourist island of Santorini on Sunday braced for the prospect of more tremors after more than 200 small earthquakes shook the site of one of the largest volcanic eruptions in recorded history,