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.

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.

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.

A new travel warning has been issued by the Foreign Office after seismic activity has been detected. Travel advice was issued for Santorini and Amorgos following increased seismic activity. The update came on Saturday and warns British travellers of an increased issue for earthquake activity.

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,