Heavy rains battering Brazil's southernmost state of Rio Grande do Sul have killed at least 83 people, authorities said on Monday, while more than 100 were still missing.

The storms have affected more than two-thirds of the nearly 500 cities in the state, leaving about 122,000 people displaced, according to the state civil defence authority.

Flooding from storms has destroyed roads and bridges in several cities, while triggering landslides and the partial collapse of a dam at a small hydroelectric power plant.

State Governor Eduardo Leite has emphasized that the death toll should still substantially increase as rescue workers gain access to more regions.

Rio Grande do Sul's civil defence said 111 people were still missing, a number that has also been increasing in the last few days. On Sunday evening, it had reported at least 78 deaths and 105 missing people.

Brazil's President Luiz Inácio Lula da Silva visited Rio Grande do Sul on Sunday with most of his cabinet and said bureaucracy would not stop the government from reconstructing the state.