Giuseppe Buzzanca, Messina's mayor, said his town had been cut off by rain and mud which had blocked roads and covered railway lines.
He has urged doctors, nurses and volunteers to go to the stricken zone to help.
Guido Bertolaso, the rescue services chief, said the impact of the rain and mud had been made worse by the spread of unregulated building.
"One house was built on the banks of a river. So what should we expect? The water follows its course and if houses are not built where they should be, this is the result," he said.
Officials blamed the overnight storm, which unleashed 25cm of rain in just three hours, but also acknowledged that deforestation and development had weakened the soil and contributed to the mudslides from Messina's surrounding hills and cliffs.
Palermo, the Sicilian capital, was also affected, with motorists stranded in their cars and a hospital's emergency services flooded.
The mudslides are Italy's deadliest since 1998, when mud submerged villages around Naples and killed 150 people.