International aid has started to arrive in Bolivia, which in recent weeks has seen its worst flooding in 25 years.
Thousands of people have been forced from their homes
The floods have killed nearly 40, with tens of thousands of people forced from their homes. Health officials have also reported outbreaks of dengue fever.
While aid has arrived, landslides are delaying the evacuation of flood zones.
President Evo Morales blames the floods on developed states failing to tackle climate change. Meteorologists say the El Nino phenomenon is the root cause.
Issuing an appeal for $9.2m, the UN described the flooding as the country's most devastating disaster ever, warning that water supplies and sanitation conditions have been severely contaminated.
The first shipment of international aid has now started arriving in Bolivia from Venezuela and neighbouring Peru, with Argentina, the United States and others also lending assistance.
The International Red Cross says that more than 350,000 people have been affected, many of them poor indigenous people in remote areas of the country.
"One of the main difficulties we're facing is actually to help proper access to the most forgotten and most affected areas," said Giorgio Ferrario, the head of the regional delegation for South America of the Red Cross.
Health officials have reported more than 1,600 cases of dengue fever and 1,400 cases of malaria since the current crisis began.
Speaking about the devastation, Mr Morales, an outspoken critic of the US, accused wealthy countries of ignoring the Kyoto Protocol which seeks to halt climate change.
He said poorer nations were being made to bear the brunt of what he described as the uncontrollable quest for industrial growth by richer ones.
This type of action, he said, demonstrated a lack of concern on the part of the developed world in altering climate change and the fate of the planet.
However meteorologists say the extensive rains are connected to El Nino, the periodic phenomenon which begins with a warming of waters in the eastern Pacific.
In its 1997 incarnation, El Nino brought drought to parts of Asia and Australia, and heavy rains and floods to Latin America.
It is not thought likely to reach the same strength this year.