MOCOA (Colombia) • Founded in 1563, Mocoa "has about 10 rivers running through it", Mayor Jose Antonio Castro was quoted as saying by the El Espectador newspaper.

"That means it is not a place where a town should be located," he said.

Its three main rivers - Mocoa, Sangoyaco and Mulato, swollen by heavy rain in nearby mountains - burst their banks last Friday, sending a wall of water, mud and debris smashing through the town.

The Red Cross estimated that 45,000 of its 70,000 residents were affected.

President Juan Manuel Santos on Monday blamed climate change for the disaster, saying Mocoa had received one-third of its usual monthly rain in just one night, causing the rivers to burst their banks.

Mr Martin Santiago, the United Nations chief for Colombia, said: "Climate change is generating dynamics and we see the tremendous results in terms of intensity, frequency and magnitude of these natural effects, as we have just seen in Mocoa."

But there are many other opinions. Some experts say deforestation in surrounding mountains meant there were few trees to prevent water washing down bare slopes. And others blame chaotic urbanisation.

The town "was the victim of a lack of urban planning", said Colombian ecologist Rodrigo Botero. "That's the case in nearly every region of Colombia."

Most of the hardest-hit neighbourhoods are poor and crowded with people uprooted during Colombia's five-decade-long civil war.

These displaced residents and their often precarious houses were hit especially hard by the disaster.

"The centralisation of society means people try to move closer to cities, no matter where it is, without considering whether a river used to flow there or if it's a ravine where rain accumulates," said architect Ortiz de Zevallos.

AGENCE FRANCE-PRESSE, REUTERS