Santorini in state of emergency after strongest quake in days of tremors

A state of emergency has been declared in Santorini after the strongest earthquake was recorded in days of near-constant tremors, which have almost emptied the famous Greek tourist haven of visitors and residents.

A quake with a magnitude of 5.2 coursed through Santorini on Wednesday evening (Thursday morning AEST), the first to exceed 5.0 since the tremors began last week.

The Greek Civil Protection Ministry on Thursday placed the island under a state of emergency until March 3 to respond to the seismic activity.

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Around 11,000 people are thought to have fled the island, which attracts more than 3.4 million tourists a year and is home to some 20,000 permanent residents.

Greek authorities have arranged additional flights to help people flee to the safety of the mainland, but evacuation efforts were complicated on Wednesday, with ferries not allowed to leave the ports due to high winds.

Normal service had resumed by Thursday.

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Sitting near the boundary of the massive African and Eurasian tectonic plates, Santorini often experiences seismic activity, but rarely so intensely for so long.

As well as Santorini, the nearby islands of Amorgos and Ios have also been shaken.

No major damage has yet been reported, but Greek authorities are taking precautions ahead of a potentially large-scale earthquake.

"The whole state mechanism has been activated and I want to urge our citizens to cooperate with the authorities," Prime Minister Kyriakos Mitsotakis said after a meeting of top officials on Wednesday.

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Santorini owes its shape to geological phenomena from millennia ago.

The island is famed for its caldera – a bowl-shaped crater caused by a volcanic eruption – which was formed by one of the largest known blasts in around 1600 BC.

Hundreds of the tremors, which have hit Santorini every few minutes for days, have had a magnitude of around 3.0 and are considered "slight" quakes.

At over 5.0, Wednesday's quake is considered "moderate."

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It was followed by at least five quakes with a magnitude of 4.0 and above, which are considered "light."

Santorini's most recent large quake – with a 7.5 magnitude – struck in 1956, killing at least 53 people and injuring more than 100 others.