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 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.

A warning of increased seismic activity in Santorini has been issued in a Foreign Office travel advisory. The alert reflected advice from the Greek Ministry of Civil Protection for the Aegean island and its smaller neighbours of Anafi, Ios and Amorgos, following more than 200 tremors registered in the area over 48 hours.

More than 200 tremors have been registered since Friday between the volcanic islands of Santorini and Amorgos, the civil protection ministry said in a statement on Sunday, citing experts tasked with assessing earthquake risks and monitoring Greece’s volcanic arc.

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,