Violent hail storms killed at least six tourists in northern Greece late on Wednesday, police said.
A Czech couple died when strong winds blew their caravan away while a Russian man and his son were killed by a falling tree, they added.
Debris from a building killed a woman from Romania.
ERT television said the region of Halkidiki, near the city of Thessaloniki, was declared a state of emergency and that the minister for citizen protection, Michalis Chryssohoidis, went to observe the rescue operation on Wednesday evening.
Temperatures in Greece have reached 37°C in the past two days, and the country was hit on Wednesday night by violent hail storms and gusts of wind, particularly in the north.
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