Gale-force winds, heavy rain and hailstorms lashed Halkidiki, near the city of Thessaloniki.

A Czech couple died when their caravan was blown away, and two Romanians and two Russians also died. A seventh body was later found in the sea.

Officials say at least 100 others were injured, with 23 people hospitalised.

A state of emergency has been declared, with dozens of rescue workers dispatched to help.

Charalambos Steriadis, head of civil protection in northern Greece, described the storm as an "unprecedented phenomenon".

It followed a spell of very hot weather in Greece with temperatures soaring to 37C (98F) over the past two days.

Winds of more than 60mph (100km/h) were recorded in the region, Reuters news agency reports.

Scenes of 'chaos'

Images and video posted on social media show trees toppled, cars overturned and buildings damaged.

Emily Kishtoo, from Surrey in the UK, was at a beach party with her family when the storm hit on Wednesday night.

"It literally came out of nowhere," she told the BBC. "The lights cut out on the beach that we were in - it was chaos.

"People running, screaming and just trying to basically get off the beach."

The damaged caravan of two elderly Czech tourists who died

Another British tourist, Holly Ellis, said windows were broken and trees downed in her hotel at Portes Beach

She says staff at the resort where she was staying with her children, aged three and five, directed the family to a bar area - which then began to flood.

"We've got two young children, there were lots of children crying, obviously very upset, very, very scared."

Electricity access at the resort has been intermittent since, she said, with no running water on Thursday morning.

Witnesses say the worst of the freak storm lasted only about 20 minutes.

The Romanian woman and her child were killed when the roof of a restaurant collapsed at Nea Plagia, officials say, while the Russian man and his son were killed by a falling tree near their hotel in the seaside resort of Potidea.

A seventh body was later found in the sea on Thursday. Formal identification is yet to take place, but a 62-year-old Greek fisherman was reported missing in the area.

Those injured are mostly tourists, officials say.

"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 which treated many of the injured.

"It was so abrupt, so sudden."

The country's newly elected Prime Minister Kyriakos Mitsotakis cancelled his schedule and is being briefed on the situation, officials say.

Defence Minister Nikos Panagiotopoulos was quoted as saying the army was ready to clear debris and would offer generators - amid reports up to 80% of the area lost its power.

This is the latest in a series of other extreme weather events across Europe in recent weeks. A heat-wave brought record June temperatures to several countries.

Golf ball-sized hail has been reported in parts of the south of France and Italy and there were forest fires in Sicily on Wednesday, including in popular beach resort areas.