Fresh overnight tremors shook Greece's top tourist island Santorini, media reports said Monday, prompting people to sleep outdoors and others to leave by plane or ferry.

Over 200 minor earthquakes were recorded at sea or on surrounding islands, with the strongest — of magnitude 4.6 — striking the waters between Santorini and Amorgos on Sunday afternoon.

An 4.2-magnitude quake was recorded at 7:10 AM (0510 GMT) on Monday northwest of the small island of Anafi, near Santorini, the Institute of Geodynamics of the National Observatory of Athens said.

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

Greek media said several people spent the night outdoors, either in their cars or areas designated as safe by the authorities.

Many left the island on flights or ferries, media reports said.

Schools on the island of some 15,500 were closed on Monday.

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

Santorini welcomed 3.4 million visitors in 2023, raising concerns over overtourism.