Dozens of boats in the Mediterranean Sea have called for emergency help.
The storm produced gusts of more than 220 km/h in some areas, the national weather agency Meteo France said on Thursday.
Two people were killed in separate incidents in Tuscany when trees were ripped up by storms on Thursday, one near the city of Lucca and another near Carrara. Another four people were injured by falling trees at a campground near Carrara.
In Corsica, a 13-year-old girl died after a tree fell in a campsite in the coastal town of Sagone. A 72-year-old woman was killed when a beach restaurant roof fell on her vehicle in Coggia, and a 46-year-old man died in a campsite in the town of Calvi.
Rescue crews found the bodies of a 62-year-old fisherman and an unidentified kayaker off Corsica's west and east coasts, according to the French maritime authority for the Mediterranean. It said both died as a result of the sudden storm and that more than 100 grounded, wrecked or stranded ships in the area have called for emergency help.
Dozens more people were injured and 12 hospitalised - one in a critical condition - and about 45,000 households were without power on Corsica, authorities said.
In Venice, high winds detached pieces of brick from St. Mark's bell tower, which stands in front of the famed cathedral. Tourists were evacuated from the structure, which was cordoned off. The storm up-ended chairs and tables in St Mark's Square and elsewhere, and swept away beach chairs on the nearby Lido.
Winds rose suddenly and were calmed within five minutes, said Carlo Alberto Tesserin, the caretaker of the Basilica and bell tower. "These were not usual winds for us," Tesserin told The Associated Press.
In northern Italy, an overnight storm forced the closures of a train line southeast of Genoa after high winds carried beach structures onto the tracks, damaging the electrical circuitry.
The storm struck during Italy's busiest beach vacation week. The mayor of Sestri Levanti, Valentina Ghio, warned that whirlwinds were possible and appealed to visitors to stay away from beaches until the severe weather had passed.
Hail the size of walnuts pummeled Italy's Liguria region with enough force to break the windows of homes and damage orchards and gardens.
Thunderstorms Wednesday flooded Paris subway stations and the Old Port of Marseille, and winds over 100 kph were recorded at the top of the Eiffel Tower during a flash flood Tuesday.
The fierce rains come amid a summer of of drought, heat waves and forest fires across Europe that scientists link to human-caused climate change.
