At least eight people died and thousands were evacuated from their homes as torrential rain battered Italy's northern Emilia-Romagna region, triggering widespread floods.
Civil Protection Minister Nello Musumeci said some areas had received half their average annual rainfall in just 36 hours, causing rivers to burst their banks, sending water cascading through towns and submerging thousands of acres of farmland.
Eight bodies had been retrieved from various locations, the vice president of Emilia-Romagna, Irene Priolo, told reporters, adding that the rains were easing but that river levels were still rising.
This weekend's Formula One race in Imola, which is close to many of the worst-hit areas, was called off after the government said the emergency services had to concentrate on the rescue operation.
"The decision has been taken because it is not possible to safely hold the event for our fans, the teams and our personnel," the Formula One organisers said in a statement.
Muddy waters flowed through the streets of Faenza, Cesena and Forli, just to the south of Imola, washing over the roofs of parked cars, submerging some stores and forcing locals to flee to the top stories of their homes.
"Do not go near the rivers. Those who live in areas close to watercourses should move to higher floors," the president of the Emilia-Romagna region Stefano Bonaccini said on Facebook.
Road and rail links were blocked in numerous locations and the mayors of many towns and cities, including Bologna, urged residents not to leave their homes.
The northern city of Ravenna, famed for its early Christian heritage sites, was also badly affected.
"It's probably been the worst night in the history of Romagna," Ravenna Mayor Michele de Pascale told RAI public radio, saying that 5,000 people had been evacuated from his city alone overnight.
It was the second time this month that Emilia-Romagna has been battered by bad weather, with at least two people dying during storms at the beginning of May.
Minister Musumeci said between 200mm to 500mm of rain fell in some parts of the region in 1-1/2 days, compared with an average annual rainfall of 1,000 mm.
Venice, further north, has not been affected.
The torrential rains followed months of drought which dried out the land, reducing its capacity to absorb water and worsening the impact of the floods, meteorologists said.