Teams in flood-ravaged southern Brazil scrambled to deliver humanitarian aid to Porto Alegre and other inundated municipalities, where queues formed for drinking water and forecasters warned of more downpours.

The worst natural calamity to ever hit the state of Rio Grande do Sul has claimed at least 95 lives, with 372 people reported injured and 131 still missing, according to the civil defence force that handles disaster relief.

“The tolls continue to rise and unfortunately we anticipate that they are still very inaccurate because the emergency is continuing to develop,” said Governor Eduardo Leite.

Nearly 400 municipalities have been hit, including state capital Porto Alegre, with more than 160,000 people forced to leave their homes after record-breaking rainfall transformed the streets into rivers.

Porto Alegre is home to some 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, remained at historic high levels on Tuesday, and officials said five dams were at risk of rupturing.

For tens of thousands of people stranded by impassable roads, collapsed bridges and flooded homes in Rio Grande do Sul, “the most urgent demand is (drinking) water,” said Sabrina Ribas, a civil defence official.

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

In Alvorada, a municipality east of Porto Alegre, people queued with buckets and plastic bottles, collecting drinking water from the few working taps. Most shops have run out of bottled water.

“This is horrible. We have children,” said 27-year-old Gabriela Almeida, queuing at a public tap with a one-year-old in her arms.

Individuals and businesses with hoses were doing what they could to help, with 48-year-old Benildo Carvalho, an Alvorada resident, filling neighbours’ bottles as a line formed outside his home.

“It’s a matter of solidarity,” he said: “You cannot deny people water.”

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

The Brazilian Navy said it would 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 said emergency funds would be freed up to tackle the crisis, vowing there would be “no lack of resources to meet the needs of Rio Grande do Sul”.

Some 15,000 soldiers, firefighters, police and volunteers were hard at work in planes, boats and even jet skis to rescue those trapped or transport aid.

Brazil’s neighbours, Uruguay and Argentina, have sent rescue equipment and trained personnel.

Celebrities have also chipped in, with footballer Neymar sending a private plane stocked with humanitarian aid. He said on Instagram he was “praying for everything to return to normal”.

But weather forecasts have shown that the flooding is unlikely to abate, with concerns being raised that the situation could worsen further.

The Inmet meteorological institute has warned of possible storms in the south of Rio Grande do Sul until Wednesday, followed by rainfall in the centre and north, which it said could imperil rescue efforts.

Weather agency MetSul said the flooding has “changed the map of the metropolitan region” of Porto Alegre.

Lula also warned the country could be forced to “import rice and beans” if harvests are delayed by the crisis, with Rio Grande do Sul being Brazil’s second-largest soybean producer and an important agricultural region.  

Meanwhile, police reports have emerged of residents refusing to leave their homes and evacuate to shelters, as looters have begun targeting empty properties.