The death toll from heavy rains that have caused flooding in Brazil's southern state of Rio Grande do Sul has risen to at least 78, local authorities said on Sunday, with more than 115,000 people displaced.

President Luiz Inacio Lula da Silva arrived in Rio Grande do Sul on Sunday morning with most members of his cabinet to discuss rescue and reconstruction efforts with local authorities.

"Bureaucracy will not stand in our way, stopping us from recovering the state's greatness," Lula said at a press conference.

"It is a war scenario, and will need post-war measures," state governor Eduardo Leite added.

Volunteers using boats, jet skis - and even swimming - have assisted in ongoing rescue efforts. In the state capital Porto Alegre, Fabiano Saldanha said he and three friends have used jet skis to save about 50 people from flood waters since Friday in islands that are part of the city.

"The only thing we hear when we enter a street is 'help,' 'help,'" Saldanha said.

The death toll could still substantially increase as 105 people were reported missing on Sunday, up from about 70 the prior day, according to the state civil defense authority. It also said it was investigating whether another four deaths were related to the storms.

Flooding from storms in the past few days has affected more than two thirds of the nearly 500 cities in the state, which borders Uruguay and Argentina, leaving more than 115,000 people displaced, according to authorities.

Floods have destroyed roads and bridges in several cities. The rains also triggered landslides and the partial collapse of a dam at a small hydroelectric power plant.

More than 400,000 people were without power on Sunday evening, while nearly a third of the state's population was without water, authorities said.

In Porto Alegre, the Guaiba lake breached its banks, hitting the highest water level on record, according to the national geological service. Porto Alegre's international airport has suspended all flights since Friday.

At a makeshift rescue center in Porto Alegre, Kaeli Moraes described being rescued along with her husband and their three children when the water had nearly reached the second floor of their house.

"There was flooding in September, then in November, and now this one. It is only getting worse," Moraes said.

In the city of Canoas, near Porto Alegre, Julio Manichesque, 76, was rescued by volunteers after he had stayed since Friday on the roof of the house where he has lived for 52 years.

"I have never seen that much water," Manichesque said.

During his weekly address to crowds in St. Peter's Square in Vatican City, Pope Francis said on Sunday he was praying for the people of Rio Grande do Sul.