By Claudia Greco and Crispian Balmer

BOLOGNA, Italy (Reuters) -At least eight people died and thousands were evacuated from their homes as torrential rain battered Italy's northern Emilia-Romagna region, triggering floods and landslides, officials said on Wednesday.

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.

This weekend's Formula One Grand Prix in Imola, which is close to many of the worst-hit areas, was called off in an effort to relieve pressure on the emergency services and prevent motor racing fans from converging on the reeling region.

"We are facing catastrophic events that have probably not been seen before," the president of the Emilia-Romagna region Stefano Bonaccini told reporters. "Extraordinary amounts of rain have fallen on land no longer capable of absorbing them."

Local authorities said flooding had hit 37 towns and communities and some 120 landslides had been registered. At least one bridge near the city of Bologna collapsed, some roads were fractured and many rail services were suspended.

Eight bodies had been retrieved from various locations, the vice president of Emilia-Romagna, Irene Priolo, told reporters, adding that although the rains were easing, river levels were still rising.

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.

The flooding followed months of drought which had dried out the land, reducing its capacity to absorb water and worsening the impact of the floods, meteorologists said.

Muddy waters flowed through the historic centres of Faenza, Cesena and Forli, washing over the roofs of parked cars, submerging some stores and forcing locals to flee to the top stories of their homes.

Drone footage from the nearby Imola Formula One circuit showed part of the paddock area under water. The race organisers said the decision to call off the Grand Prix had been taken "because it is not possible to safely hold the event for our fans, the teams and our personnel".

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.

"Ravenna is unrecognisable for the damage it has suffered."

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.

(Reporting by Angelo Amante, Crispian Balmer and Alvise Armellini, Writing by Crispian Balmer; Editing by Gareth Jones, Emelia Sithole-Matarise and Toby Chopra)