Earthquakes rattled Greece’s volcanic island of Santorini every few minutes through the night and into Wednesday as authorities bolstered their emergency plans in case the temblors are a harbinger of a larger quake to come.

According to officials, more than 11,000 people have left Santorini, with around 7,000 departing by ferry and 4,000 people leaving by air. Hundreds of earthquakes have rocked the island, the strongest of which was a magnitude five tremor on Tuesday.

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.