An aerial view shows a partially collapsed building and debris-covered roads in the village of Scaletta Zanclea, near the Sicilian town of Messina on Friday. (Guardia Di Finanza/Reuters)

Rivers of mud unleashed by heavy rains flooded parts of the Sicilian city of Messina, leaving at least 20 people dead and several still missing, Italian officials said Friday.

Another 40 people were hospitalized after mudslides swept away cars and caused several buildings to collapse overnight as entire villages and suburbs on the island's eastern coast were flooded, civil protection chief Guido Bertolaso told reporters.

Several more people were believed to be missing but authorities gave varying figures, ranging from five to 20.

The government in Rome declared a state of emergency for the area, freeing funds for emergency relief and reconstruction.

Rescuers with sniffer dogs were searching for the missing in hard-hit suburbs and surrounding villages, although efforts were hampered because many roads and railways have been obliterated by the mud flows, Messina Mayor Giuseppe Buzzanca told Italy's Sky TV.

Many of the injured had to be taken to hospitals by sea, while some of the hardest-hit areas were still reachable only on foot or by helicopter.

20 missing

Buzzanca said there were 20 people missing, while Fortunato Romano, the city's civil protection head, told Sky later Friday that five or six were still being sought.

The mud swept into the Messina area from surrounding hills and cliffs, clogging streets with grime and debris that reached as high as the door handles of cars and homes.

Officials blamed the overnight storm, which unleashed 25 centimetres of rain in just three hours, but acknowledged that deforestation and development had weakened the soil and contributed to the mudslides from Messina's surrounding hills and cliffs.

Vegetation is essential to holding sloping terrain together during rain.

The landslides were Italy's deadliest since 1998, when a rain-drenched mountain near Naples unleashed a torrent of mud that submerged villages and killed 150.

As the rain subsided Friday, residents and firefighters started clearing the mud with shovels and bulldozers.

Among the 20 killed was a man who was submerged and suffocated in the mud on the main piazza of a southern Messina suburb, the ANSA news agency said. Another man drowned in the flooded cellar of his country home, it said.