The storms have caused floods which destroyed bridges and buildings, turning streets into rivers and leaving more than 163,000 displaced in Rio Grande do Sul, which borders Uruguay and Argentina.
According to the state civil defence authority on Wednesday, 128 people are still missing.
"We've lost everything," said Adriana Freitas, in state capital Porto Alegre.
"It's sad when we see the city, our house, in the middle of the water; it seems like it's over, that the world has ended."
Brazil's national centre for natural disasters said on Tuesday that the southern area of the state was under "high risk" of more floods on Wednesday, with rainfall expected to restart.
Although it is not expected to be significant in volume terms, water levels are already high in many places, and the soil saturated.
Weather forecaster MetSul said in a statement the region could face more "very large" floods "of serious proportions".
Government officials reiterated that help was coming for Rio Grande do Sul, with the federal government saying it would soon announce credit lines to assist companies, farmers, cities and the state government.
"We understand the difficult financial situation faced by Rio Grande do Sul," President Luiz Inacio Lula da Silva said at an event in Brasilia, adding he wanted to make sure the state would get "everything it is entitled to".
"We still don't know the exact dimension of the floods, that will only be clear to us when the water levels return to normal," Lula said.
Civil defence figures showed that 417 of Rio Grande do Sul's 497 towns have been affected by the heavy rains.
