The total death toll from widespread storms hitting Italy is at least 30, officials announced on Sunday.
Two families have been killed in Sicily after a river burst its banks and a sea of mud submerged their house.
Nine people died in the incident in the village of Casteldaccia - from children aged one, three and 15 to their grandparents. Only three people who were outside the house at the time survived.
They were living in a building that had been built illegally, according to the Italian news agency ANSA.
Palermo's regional administrative court (TAR) said the villa that housed the victims should have been demolished.
In the island's mountainous areas, rainfall and runoff can take many hours or even days to fill area rivers before the water flushes towards the sea, impacting coastal communities.
Videos from social media showed widespread devastation with cars and debris littering the streets of the village.
Italian Prime Minister Giuseppe Conte spoke of "an immense tragedy" during a visit to the island, as he flew over the worst-hit areas by helicopter and met survivors of the families.
Three other people died when their cars were blown away elsewhere in Sicily.
Torrential rain triggering landslides and floodwaters led to the fatalities people in the region around Palermo, a spokesman for the Sicilian capital's Prefecture said on Sunday.
"There are still some people missing," he added.
Heavy rains and strong winds have been battering Italy for at least a week, uprooting millions of trees and cutting off villages and roads.
Some of the worst damage has been recorded in the regions of Trentino and Veneto.
Italian regions have been counting the severe impact of the storms, particularly the six northern regions placed under red alert for several days.
Conte announced one billion euros in funding to fix "hydrogeological instability" across the length and breadth of Italy. Interior Minister and League leader Matteo Salvini asked for 40-billion euros.
The centre-left Democratic Party blamed many of the deaths on amnesties on illegal buildings over the years, some of them voted for by the League.
Salvini said that "armchair environmentalism" was to blame, preventing trees from being cut down and water courses altered to reduce the risk.
Conte announced that a cabinet meeting would take place this week to declare a state of emergency and will come up with the first package of aid for areas affected.
Economy Undersecretary Massimo Garavaglia said funds to remedy hydrogeological instability would be included in the 2019 budget bill.
Environment Minister Sergio Costa said, "we need a fast norm to demolish illegal and dangerous buildings. A special group will study the problem. Illegal building has a very old history in Italy."