Torrential rain drenched northern Italy again Monday as the damage suffered by just one of the regions hit by floods and landslides was put at one billion euros ($1.25 billion).

In Sesto Calende, a small town near Lake Maggiore and the Swiss border, the central square resembled a giant pond, a handful of sandbags doing a poor job of preventing the water from soaking the ground floors of houses and businesses.

"It is a nationwide problem caused by decades of neglect and poor governance," said one resident, Mauro, with a resigned shrug.

A total of 12 people have died in weather-related accidents in northern Italy since mid-October.

Three deaths at the weekend included a pensioner and his granddaughter who were buried alive when a landslide hit their house on the shores of Maggiore in the early hours of Sunday morning, the third tragedy of its type in less than a week.

Claudio Burlando, the president of the Liguria region, which includes the entire Italian Riviera, said the damage incurred on his patch alone in the last month now exceeded one billion euros.

Apart from the clean-up costs, millions of euros worth of crops have been destroyed and many fields rendered unsuitable for grazing or planting, while motorways and other infrastructure, including a Genoa cemetery where zinc coffins were washed away at the weekend, will have to be repaired at public expense.

Most costly of all, the water-management systems which have proved incapable of dealing with exceptional conditions will have to be upgraded.

Visiting the Ligurian capital of Genoa, Cabinet Secretary Graziano Delio said current constraints on state spending would be waived to ensure local governments do this.

"The stability pact (austerity programme) will not be a problem for those who have suffered catastrophes," he said, adding that the government had earmarked three billion euros to provide interest-free loans to local authorities planning repair work.

"We want mayors to know they must not fear making investments for the sake of (water) security," he said.

Liguria's Burlando welcomed the move but said Italy's central government had to accept some of the blame now being piled onto to local authorities.

In particular, he said, regular amnesties which ensure retrospective planning permission for unauthorised construction had resulted in a huge number of residences and other buildings being erected in places where they contribute to making slopes less secure and stable, often because trees were removed.

Forecasters said there would be no let-up until Wednesday, raising fears that the region's main river, the Po, could burst its banks.