Two families have been killed in the same house in Sicily when the torrential rains and high winds lashing Italy caused a river to burst its banks, drowning the nine people inside and bringing the total death toll to at least 29.

Key points:

• The tragedy brings the number of people killed in Italy to at least 29, with 12 in Sicily
• Italian media say a 1-year-old, a 3-year-old and a teenager were among the dead
• Italy has earmarked $395 million for disaster relief

Rushing water filled the villa in Casteldaccia in the province of Palermo in moments, killing the families who were spending Saturday night there.

A father and his daughter escaped harm because they had left the house to do some shopping while a third person climbed a tree to survive.

Italian news reports said the dead included a 1-year-old, a 3-year-old and a teenager.

The tragedy brings the number of people killed in Sicily this weekend to at least 12 after three other people died in their cars when hit by torrents of water.

Italian Prime Minister Giuseppe Conte spoke of "an immense tragedy" during a visit on Sunday to affected areas in Sicily.

He said a cabinet meeting would be convened this week to declare a state of emergency and come up with the first package of aid for areas affected.

Heavy rains and gale-force winds have battered Italy for several days, uprooting millions of trees and cutting off villages and roads.

Italy's Civil Protection Agency said deaths caused by the wave of bad weather stood at 17, excluding the fatalities in Sicily.

Some of the worst damage was recorded in the country's northern regions of Trentino and Veneto.

Drone footage emerged on Sunday revealing the extent of destruction to roads, buildings and boats around the northern port town of Rapallo.

On Saturday the governor of Veneto, Luca Zaia, said storm damage in the region amounted to at least a billion euros.

During a visit on Sunday to badly-hit areas in the north, Italy's Interior Minister Matteo Salvini said 250 million euros ($395 million) had already been earmarked for relief.

He said the government would be asking to use special EU funds.

Mr Salvini, who is also Deputy Prime Minister, said a rough estimate of how much it would cost to safeguard Italy against such events was 40 billion euros ($63.45 billion).