One woman was reported dead in southern Sardinia, where hours of heavy rain have swollen rivers dangerously high, flooding houses and sweeping away part of a motorway bridge.

The victim, aged 45, was driving near the town of Assemini with her husband and three children when high water blocked their car. They became separated as they tried to escape and while the rest of the family was rescued by police, the woman's body was recovered on Thursday.

Part of a state road that runs over the Santa Lucia river collapsed on Wednesday, cutting the highway in two. No cars were on the bridge, which links the capital Cagliari to the town of Capoterra, at the time: it had been closed to traffic as a sink hole opened up earlier in the day.

Photo: Vigili del Fuoco/AFP

One woman in labour had to be flown to hospital as the roads remain impassable, police said.

More than 100 firefighters were at work around in the Cagliari area to rescue people trapped, with some people taking shelter on the roofs of their homes or vehicles.

At least one person, a shepherd, is reported to be missing.

Across the southern half of the island, schools, public offices and parks were ordered closed throughout Thursday, while trains from Cagliari were cancelled.

Similar precautions were in place on the mainland in Liguria, where the provinces of Imperia and Savona are on red alert and the rest of the region on orange. 

Fierce storms were expected to batter north-west Italy throughout Thursday, with heavy rain, strong wind, hail and thunder on the forecast.

The bad weather is expected to reach parts of Piedmont and Lombardy, as well as the Tuscan coast and Emilia-Romagna. The coast of Lazio, the region of Rome, has also been placed on yellow alert, as have parts of Sicily and Calabria in the south, where floods last week claimed the lives of a mother and her young son.