The death toll from devastating floods that have ravaged southern Brazil for days reached 100 on Wednesday, authorities said, as the search continued for dozens of people still missing.

Nearly 400 municipalities have been affected by the worst natural calamity ever to hit the state of Rio Grande do Sul, with hundreds of people injured and 160,000 forced from their homes.

Many have no access to drinking water or electricity -- or even the means to call for help with telephone and internet services down in many places.

On Tuesday, state governor Eduardo Leite had warned the human toll was likely to rise as "the emergency is continuing to develop" in the state capital of Porto Alegre and other cities and towns.

Some 15,000 soldiers, firefighters, police, and volunteers were at work across the state, many in boats, and even jet skis, to rescue those trapped and transport aid.

Authorities urged people not to return to affected areas due to possible landslides and health hazards.

Many people are loath to leave their homes for the safety of shelters amid reports of abandoned properties being looted.

"Contaminated water can transmit diseases," civil defense spokeswoman Sabrina Ribas warned on Wednesday.

The National Confederation of Municipalities said nearly 100,000 homes had been damaged or destroyed by unprecedented rains and floods in the state, with losses estimated at about 4.6 billion reais (more than $900 million.)

Porto Alegre is home to about 1.4 million people and the larger metropolitan area has more than double that number.

The state's Guaiba River, which runs through Porto Alegre, reached historic levels and five dams are at risk of rupturing.

  'A parallel universe' 

 There were queues at public taps and wells as officials warned that the most urgent need of people stranded by impassable roads, collapsed bridges and flooded homes was drinking water.

Only two of Porto Alegre's six water treatment plants were functioning, the mayor's office said Tuesday, and hospitals and shelters were being supplied by tankers.

Helicopters were delivering water and food to communities most in need, while work continued on restoring road access.

The Brazilian Navy was to send its "Atlantic" vessel -- Latin America's largest -- to Rio Grande do Sul on Wednesday with two mobile water treatment stations.

President Luiz Inacio Lula da Silva has vowed there would be "no lack of resources to meet the needs of Rio Grande do Sul."

In Gasometro, a part of Porto Alegre popular with tourists, the water continued to rise Wednesday, complicating rescue efforts.

"You can only cross on foot or by boat. There is no other way," 30-year-old resident Luan Pas told AFP next to a street turned into a stagnant, smelly river.

Operations at the port of Porto Alegre have been suspended, and its international airport indefinitely closed.

The Air Force said the military base outside town will receive commercial flights transporting aid and passengers.

In a rare dry spot in Porto Alegre's historic center, dozens of people gathered around a generator rented by a pharmacy to charge their cell phones.

"This is a parallel universe," said one of them, university professor Daniela da Silva, 30.

The Inmet meteorological institute has warned of more storms with heavy rains and winds in the south of the state and downpours over the weekend in the Porto Alegre region.

The World Meteorological Organization in a report Wednesday, said Latin American and the Caribbean had recorded its warmest year on record in 2023 -- "a year of record climatic hazards" for the region due to climate change and the El Nino weather phenomenon.

Many towns and cities in Brazil, it said, were hit by "exceptional rainfall" that caused displacement and massive upheavals.

Due to climate change, extreme or rare events "are becoming more frequent and more extreme," Jose Marengo, research coordinator at Brazil's National Center for Natural Disaster Monitoring (Cemaden) told AFP.

According to weather agency MetSul, the flooding has "changed the map of the metropolitan region" of Porto Alegre.