Two young people died south of Rome when a tree crashed onto the car they were travelling in, while another person was killed and several injured in the nearby town of Terracina after gale-force winds brought down pine trees.
A 21-year-old man was killed by a falling tree as he was walking near Caserta, in Naples.
In Liguria, a woman died after being struck by debris blown off a building.
The national Civil Protection Department issued a red alert – the highest level – on Monday morning for six regions: Abruzzo, Liguria, Lombardy, Veneto, Friuli-Venezia Giulia and Trentino-Alto Adige.
More wild weather is expected today in these regions, with torrential rain and a risk of landslides in Alpine areas.
Many schools and roads were closed, while local authorities urged people not to travel unless necessary.
Many tourist sites – including the Roman Forum, the Colosseum, and Pompeii – were also closed to the public.
Venice vaporetto services were suspended as water inundated the lagoon city, submerging 75 per cent of its historic centre.
Local authorities said the high tide hit a maximum of 156 centimetres in early afternoon – the fourth-highest level ever recorded.
Meanwhile, an orange alert – the second highest level – was issued for Piedmont, Emilia-Romagna, Tuscany, Marche, Umbria, Lazio, Calabria, Sicily, and parts of Molise, Campania, and Puglia.
