More than 600 people have also been displaced, according to a statement released by the State Civil Defense, which earlier said that at least seven children were among the dead.
Authorities have deployed a working group of firefighters, military police and civil defense personnel to support the mayors of the cities that have been impacted, said São Paulo Governor João Doria on Sunday.
Images from the municipality of Franco da Rocha showed parts of major roads submerged, while others showed rescue workers digging through debris in search of survivors and valuable belongings after a landslide destroyed homes.
Some 15 million reais (about $2.8 million) will be allocated to the 10 most-affected municipalities, according to a statement from Doria’s office.
“(The funds) may be used to repair chronic urban problems in the municipalities that generate inconveniences such as flooding points and landslides,” the statement said.
The intensity and frequency of extreme rain events and flooding are expected to increase in this area the more the Earth warms.
Northeastern Brazil has also been battling heavy rains since December.