At least 12 people have died, five are missing and nearly 3,000 have been left homeless after an "extratropical cyclone" hit Brazil's Rio Grande Do Sul, local authorities say.

Traveling to the region's hardest hit regions, government authorities have reinforced the role of the state's relief structure and called upon "the solidarity of the population."

Rio Grande Do Sul's governor Eduardo Leite said that the Military Firefighters Corps conducted around 2,400 rescues over the past two days, with operations still underway.

"Our priority at the moment is to find the missing and save people who may still be stranded by the floods." Leite wrote in a statement. "We have all our teams in the field, and the Secretariat for Logistics and Transport is already analyzing compromised bridges and roads so that we can act in an urgent manner and provide free passage in these locations."

One video showed a man and dog being rescued by helicopter from the flooding.

The federal government has committed to offering humanitarian aid and supporting reconstruction efforts.

Extreme weather around the world is becoming more intense and more frequent against the backdrop of a fast-warming climate.

The world is already 1.2 degrees Celsius warmer than it was in pre-industrial times, and the next five years are predicted to be the hottest on record.

The proportion of high-intensity hurricanes, or tropical cyclones, has increased due to the warmer global temperatures, according to the UN.

Scientists have also found that the storms are more likely to stall and lead to devastating rainfall and they last longer after making landfall.