At least six people died and many more were injured in storms that hit northern Greece, state broadcaster ERT reported early on Thursday.
Tourists from the Czech Republic, Romania and Russia were among those who died in the storms. Two of the victims were children.
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Dozens of people were injured after strong winds swept across the northeastern peninsula of Halkidiki, leaving destruction behind that included uprooted trees, collapsed roofs and overturned vehicles.
"It is the first time in my 25-year career that I have lived through something like this," said Athansios Kaltsas, director of the Nea Moudania Medical Centre, where many of the injured were receiving treatment.
"It was so abrupt, and so sudden," he added.
Six who died were all tourists
Two of the victims were elderly Czech tourists who were killed when strong winds and water destroyed their camper van, according to police.
A woman and an 8-year-old boy, both Romanian nationals, were killed after a roof caved in at a restaurant in Nea Plagia.
Two Russian nationals, one of whom was a boy, also perished after a tree collapsed near their hotel in the coastal town of Potidea, authorities confirmed.
"Six tourists were killed and at least 30 people were injured during this cyclone," Charalambos Steriadis, head of civil protection in northern Greece, said.
Steriadis added that Halkidiki had declared a state of emergency.
Weather of this kind is not the norm in Greece at this time of year, when it is typically hot and dry. Meteorologist Klearxos Marousakis described the conditions as "extremely unusual."
Indeed, the tornadoes and hailstorms that caused the destruction came after a period of hot weather, with temperatures as high as 40 degrees Celsius (104 Fahrenheit).
jsi/sms (AFP, dpa, Reuters, AFP)
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