Heavy flooding and landslides have killed at least 36 people, according to authorities in the Brazilian state of So Paulo, forcing some cities to postpone their annual Carnival celebrations.
Video showed flooded highways, submerged neighborhoods, and debris from swept-away homes.
Roads have been blocked, and rescue teams have had difficulty finding survivors.
In some places, Sunday's rainfall exceeded 600mm (23.06 inches), which is twice the monthly average.
Felipe Augusto, the mayor of the badly affected town of So Sebastio, said, "Search and rescue teams are not managing to get to several places; it is a chaotic situation.".
The extent of the damage is still unknown to us. We're attempting to save the victims. ".
Mr. Augusto continued, saying the situation was still "extremely critical," adding that there were dozens of people still missing in the town and about 50 houses had collapsed and been destroyed.
At least 35 deaths were reported in So Sebastio by the state government, and a young girl's death was reported in Ubatuba, 80 km (50 miles) to the northeast. Many hundreds have been evacuated and displaced.
A civil defense official told the newspaper Folha de So Paulo, "Unfortunately, we are going to have many more deaths.".
In the meantime, authorities claim that 338 more people had to be evacuated from coastal areas north of So Paulo, leaving another 228 people without a place to live.
In six towns in the state—So Sebastio, Caraguatatuba, Ilhabela, Ubatuba, Guarujá, and Bertioga—a 180-day state of calamity was proclaimed.
Tarcsio de Freitas, the governor of the state, declared that he had released the equivalent of $1.5m (£1.2m) in funding to help with disaster relief.
The northern coastline, which is a popular destination for wealthy tourists trying to avoid the intense street celebrations in the major cities, had all of its Carnival events canceled.
The festival, which typically lasts for five days in the lead-up to the Christian festival of Lent, is known for its vibrant celebrations and is closely associated with Brazil.
According to local media, Santos, Latin America's largest port, was also closed due to wind gusts over 55 km/h (34 mph) and over 1-meter-high waves.
The affected areas would be visited by the president on Monday, according to Luiz Inácio Lula da Silva, who was spending the weekend of the carnival in the state of Bahia in the northeast.
He expressed his sympathy to those who had lost loved ones in a tweet and pledged to coordinate with the relevant authorities to send out rescue teams and medical care.
In his letter, Mr. da Silva stated: "We are going to gather all levels of government and, with the solidarity of society, treat the injured, look for the missing, restore highways, power connections, and telecommunications in the region.
Emergency teams could face even more challenging conditions as more intense rain is predicted to fall nearby.
As the effects of climate change set in, it is anticipated that extreme weather events like the floods would become more frequent.
More than 230 people were killed by torrential rain in the city of Petropolis in the southeast last year.