Images showed muddy brown waters rising as high as rooftops.
Organisers concede more efforts were necessary to handle the heat, which hit 59C on the heat index.
"Our main objective at this first moment is to protect and save human lives."
"A tragedy like this is unacceptable, an absurd act of hate and cowardice...an act of violence against innocent and defenseless children."
Rescue workers continue to look for victims, reconnect isolated communities and clear roads.
Lula defeated Jair Bolsonaro in October to win an unprecedented third presidential term
Lula had 50.8 percent of votes compared with 49.2 percent for Bolsonaro.
One of President Jair Bolsonaro's closest associates was filmed chasing a supporter of rival candidate Luiz Inacio Lula da Silva with a gun.
The winning candidate needs at least 50 percent of the votes
