Rescuers were searching the area for any casualties after neighbors reported hearing screams, the ANSA news agency reported.
Most of a hill in the Aurelio district, a suburb between the Vatican and Rome's city limits, collapsed under heavy rain and swallowed up the homes. Officials said many of the inhabitants are believed to be Roma, also known as gypsies.
Six people who were swept away in Rome with their makeshift shelters during a landslide were found in good condition, ANSA said.
Emergency officials said they fielded 3,000 calls for aid in only a few hours Friday morning after the Italian capital was swamped by torrential rains and floods.
Heavy rain and snow pounded much of Italy Friday and Rome, Pisa and Florence braced for flooding as rivers climbed beyond their banks.
Officials said about 1,000 people were evacuated from structurally unsound buildings in San Miniato because of overflowing rivers and streams, ANSA reported.
Emergency officials said the Arno River was "constantly leaving its riverbed" and flooding areas in its path.