Four other people were still missing from the ship that was carrying 100 participants although it had a capacity limit of 40, firefighters said yesterday.
Firefighters had accompanied the procession but the accident took place as the boats were returning to their ports, a spokesman said.
"The boat was participating in the procession, which takes about two hours in the Amazonian state of Amapa, and must have capsized after hitting a sandbar upon its return," firefighter commander Miguel Rosario told AFP.
Brazil's most famous procession, the Cirio de Nazare, occurs in the Amazonian city of Bethlehem, with about two million participants.