Heavy rains in the southern Brazilian state of Rio Grande do Sul killed 39 people, with another 68 still missing, the state civil defence agency said on Friday, as record-breaking floods devastated cities and forced thousands to leave their homes.

It was the fourth such environmental disaster in a year, following floods in July, September and November 2023 that killed 75 people in total.

According to the Brazilian Geological Service, the flooding state-wide has surpassed that seen during a historic 1941 deluge.

The agency said that in some cities, water levels were at their highest since records began nearly 150 years ago.

On Thursday, a dam at a hydroelectric plant between the cities of Bento Goncalves and Cotipora partially collapsed, and entire cities in the Taquari River valley, like Lajeado and Estrela, were overtaken entirely by water.

In the town of Feliz, 50 miles from the state capital, Porto Alegre, a massively swollen river swept away a bridge that connected it with the neighbouring city of Linha Nova.

Operators reported electricity, communications, and water cuts across the state. According to the civil defence agency, more than 23,000 people had to leave their homes.

Without internet, telephone service or electricity, residents struggled to provide updates or information to their relatives living in other states.

Helicopters flew continually over the cities while stranded families with children awaited rescue on the rooftops.

The downpour started on Monday and is expected to last at least through Saturday, Marcelo Seluchi, chief meteorologist at the National Centre for Monitoring and Alerts of Natural Disasters, told Brazil’s public television network on Friday.

On Thursday night, governor Eduardo Leite alerted the state’s population – known as gauchos – about the persistence of rains and floods.

He said the situation was expected to worsen in Porto Alegre.

“As a human being, I am devastated inside, just like every gaucho is,” he said.

“But as governor, I am here steadfast and I guarantee that we will not falter. We are doing everything with focus, attention, discipline, and outrage, to ensure that everything within our reach is done.”

Weather across South America is affected by the climate phenomenon El Nino, a periodic, naturally occurring event that warms surface waters in the Equatorial Pacific region.

In Brazil, El Nino has historically caused droughts in the north and intense rainfall in the south.

This year, El Nino’s impacts have been particularly dramatic, with a historic drought in the Amazon.

Scientists say extreme weather is happening more frequently due to human-caused climate change.