Greece ’s top tourist island has been forced to shut its schools on Monday due to an increase in seismic activity in the area. Authorities have advised people on the Aegean island of Santorini to also avoid two small ports and refrain from gathering in indoor spaces after increased tremors in the area over recent days.

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.

Schools on Santorini have been forced to close down following an increase in seismic activity in the area. The Greek Ministry of Civil Protection has issued advice for residents and visitors to both Santorini and Amorgos – and now the UK Foreign Office has echoed that advice for any Brits visiting or living there.

Greece sits on multiple fault lines and is often rattled by earthquakes. Santorini is visited by about three million people annually, including many British tourists. One of the largest volcanic eruptions in history, around 1600 BC, formed the island in its current shape, while the last eruption in the area occurred in 1950.

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.

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.