More than 200 tremors near the island of Santorini have prompted Greek authorities to close schools and tell residents to avoid some ports and drain swimming pools.
Earthquake experts say the increase in seismic activity around the Aegean tourist island - known for its whitewashed buildings and black-sand beaches - is not related to volcanic activity.
Greek Prime Minister Kyriakos Mitsotakis chaired an emergency meeting in Athens, as Santorini authorities prepared for a potential evacuation.
Tents have been set up in an outdoor stadium, police and the fire brigade have been put on alert and special disaster response units with sniffer dogs are on standby.
Island residents have been advised to avoid large open-air events and to stay away from four small ports including the harbour of Fira, which mainly serves cruise ships.
Home and hotel owners have also been told to drain their swimming pools over concerns that large volumes of water could destabilise buildings in the event of a strong quake.
Schools will be closed on Monday in Santorini as well as on the nearby islands of Amorgos, Ios and Anafi.
More than 200 tremors have hit since early on Friday but there have been no reports of damage or casualties.
The strongest earthquake recorded was magnitude 4.6 on Sunday afternoon, while a few tremors of over magnitude 4 and dozens of magnitude 3 have followed.
Read more from Sky News:
Slimming World founder dies in Majorca
Farmer who shot burglar dead in 1999 dies
Experts said it was impossible to predict whether the seismic activity could lead to a stronger tremor, but added that the area could potentially produce a 6-magnitude quake.
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.
(c) Sky News 2025: Greek island Santorini on earthquake alert after more than 200 tremors
US secretary of state says Panama must reduce Chinese influence on canal or face consequences
Aston Villa sign Marcus Rashford on loan deal from Manchester United
Sir Keir Starmer to urge EU nations to 'shoulder more of the burden' on defence spending
University of Essex students named as victims after car crashed into building in Colchester
Farmer Tony Martin, who shot burglar dead in 1999, dies aged 80
'Shocking, Misplaced And Reckless': Village Residents Hit Out At Housing Plan
Highest Number Of Police Officers For Hampshire And Isle Of Wight Constabulary In A Decade
Emergency Services Called To Newport Petrol Station After Car Crashes Into Kiosk
"There's Likely To Be In Excess Of 200 Redundancies": Island Trade Unionists On School Plans