Cyclone Cleopatra:

: A damaged street in Uras, central Sardinia, after Cyclone Cleopatra hit. 

A state of emergency has been declared after at least 18 people were killed by a cyclone on the Italian island of Sardinia.

The north of Sardinia took the brunt of Cyclone Cleopatra, with 450 millimetres of rain falling in 90 minutes.

In the worst storm in decades, rivers burst their banks, cars were swept away and bridges collapsed in the towns of Olbia and near Nuoro.

Among the dead is a family of four who were in their ground floor apartment when the flood waters came through.

A police officer died when a bridge collapsed as he was escorting an ambulance over it.

A number of people are still unaccounted for, while hundreds have been forced from their homes.

The Red Cross has set up temporary accommodation in sports halls and other centres.

"This is a national tragedy," prime minister Enrico Letta said.

The declaration of a state of emergency will allow resources to be freed up more quickly to reach devastated areas, with swathes of the island under muddy flood waters that covered cars and swamped houses, displacing 2,700 according to authorities.

The mayor of Olbia, the north-eastern Sardinian town among the worst-affected areas, said the sudden flooding had burst "like a bomb" with the same amount of water falling in 90 minutes as falls in the city of Milan in six months.

Mayor Gianni Giovannelli said houses across the area had been left half-submerged by the floods and rescuers were still searching for possible victims.

"We've just found a dead child we had been searching all night for," he told SkyTG24 television.

Residents told of narrow escapes as sudden floods of water surged into their houses.

"We managed to open the door with all this water inside, it was just devastating," Olbia resident Francesco Brandano said.

"The kids didn't have anything, they were naked, naked, they managed to get out by the back stairs.

"Everything is wet, everything needs to be thrown away. Everything is gone, documents, everything.

"We haven't got anything left."