SANTORINI, Greece: Tourists and locals have been forced to flee the Greek holiday island of Santorini on Monday after it was hit by “intense” tremors for a fourth day in a row.

Quakes, some with a magnitude of over four, shook the popular destination’s narrow streets and white-washed villas every few minutes on Monday as people were told to avoid crammed indoor spaces.

Kyriakos Mitsotakis, Greece’s Prime Minister, said: “I want to ask our islanders above all to remain calm,” adding that authorities were monitoring the “very intense” geological phenomenon.

Footage filmed overlooking the island’s steep cliffs captured multiple rock slides tumbling into the crystal clear waters. Since Friday, hundreds of tremors have been recorded between the volcanic islands of Santorini and Amorgos in the Aegean Sea, forcing authorities to announce school closures on both islands, as well as on the nearby Ios and Anafi.

Additional flights were scheduled at the request of the Greek government to help people leave the island, which is part of an ancient volcanic caldera. Efthymios Lekkas, a professor of tectonic geology who is part of a team of experts assessing the situation on the ground, told Greek television: “We estimate it (the tremors) will continue for some days and there could be a lengthy seismic sequence.”