STORY: Rescuers rushed to evacuate people stranded by devastating floods across the southern Brazilian state of Rio Grande do Sul on Tuesday.

The deluge has left at least 90 dead and over a hundred and fifty thousand homeless, with many desperate survivors seeking food and basic supplies.

Relatives waited at the shore of the Guaiba River, in the state capital of Porto Alegre, to find their loved ones on the boats that brought rescued people from flood-hit areas.

Taina Silva is still waiting for news on her husband:

"My daughter doesn't stop crying. There are firefighters there but they say they can't do anything from there to here, so I should come here and ask the firefighters here if they can save my husband there."

The flooding has made rescue efforts even tougher, with dozens of people still waiting to be evacuated by boat or helicopter from rain-stricken homes.

The downpour that began last week has caused rivers to flood, inundating whole towns, destroying roads and bridges, and airports.

Now the rain is forecast to let up on Thursday... but then will continue through the weekend.

Experts say it's driven by a heatwave caused by this year's El Nino phenomenon meeting a cold front coming off the Antarctic and unusual humidity in the Atlantic.

In Porto Alegre, a city of 1.3 million inhabitants, downtown streets were under water after the Guaiba River breached its banks with record water levels.

Civil Defense authorities say the floods have also impacted water and electricity services, with more than 1.4 million affected overall.