Speaking from Brussels, Mitsotakis said authorities were monitoring a "very intense" geological phenomenon over recent days, adding: "I want to ask our islanders above all to remain calm."

Known for its spectacular cliffside views and a dormant volcano, Santorini and neighbouring Aegean Sea islands have been hit by hundreds of tremors since last week, the largest with a magnitude of 4.9.

The neighbouring islands of Anafi, Ios and Amorgos have also been affected.

The activity has prompted authorities to send rescue units to the area and close schools, and some areas have been declared off-limits because of rockslide risks.

Britain issued a travel warning, urging its nationals to follow the advice of local officials.

Greek authorities have also asked people to avoid large gatherings in enclosed spaces and stay away from certain ports, derelict buildings and empty swimming pools.

Efthymios Lekkas, president of the Organisation of Antiseismic Planning and Protection, told public broadcaster ERT on Monday that there was a "faint possibility of a 5.5-magnitude earthquake", but ruled out one measuring over six.

Many among the population of over 15,000 spent the night outdoors, while others are leaving the island by sea and air.

The Aegean Sea is prone to earthquakes. In 1956, a quake with a magnitude of over 7.0 left over 50 dead on Santorini and gutted hundreds of buildings.

Kostas Sakavaras, a tourist guide who has lived on the island for 17 years, told AFP he had never experienced this level of seismic activity before.

"It was shaking every three to four hours yesterday. This feels different from the other times," he said.

Sakavaras said he left the island on Sunday with his wife and two children, on a ferry that was full.

"We plan to stay (on the mainland) until the end of the week. I think it's going to escalate tomorrow and I hope then it will calm down," he said.

A Greek coastguard source said over a thousand people had left the island by sea on Sunday.

Aegean Airlines, Greece's biggest carrier, said it had dedicated additional flights to and from Santorini after a request from the country's civil protection ministry.

"We are worried, we all want to leave... mainly for the children," said Dimitris, a local labourer queuing outside a ferry ticket office.

Santorini is among Greece's premier travel destinations, with 3.4 million visitors in 2023.

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Aegean Airlines