The president of the Lazio region surrounding Rome, Nicola Zinagaretti said was deciding whether to declare a state of emergency.
In the capital, emergency services received some 3,000 calls, as people were forced to climb into the roofs of their homes and cars in some areas as up to 130 millimetres of rain fell in a matter of hours.
A heavily pregnant woman who went into labour had to be taken to hospital in a dinghy, while six homeless people including Roma Gypsies and other immigrants were rescued from makeshift huts in an area of the city not far from the Vatican after a mudslide engulfed their makeshift huts.
Northern neighbourhoods in the Italian capital were flooded and authorities were monitoring the Tiber river, at risk of overflowing. Several roads and metro stations had to be closed and and mud and detritus cause a train to derail between Rome and Viterbo.
Weather alerts were also issued in Tuscany, 1,000 people were evacuated in the province of Pisa and the city itself was partly flooded, forcing emergency workers to erect barriers and reinforce banks to channel water to the sea. In the town of Volterra a 30-metre section of medieval walls collapsed.
In Florence, the river Arno was reported to be at a 20-year high although the city's mayor Matteo Renzi said the river was not in danger of bursting its banks. Small towns outside Florence and nearby Prato were virtually surrounded by rising flood water as schools closed for the day.
In the lagoon city of Venice, exceptionally high tides were expected to submerge half the city at around midnight.
Across the Adriatic in Serbia, dozens of people remained stranded in snow and rescue teams were struggling to reach those trapped on a 30-kilometre stretch of road some 60 kilometres north of Belgrade after gale force winds formed four-metre-high snowdrifts on the road, emergency services said.