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MOCOA, Colombia — Jose Albeiro Vargas last saw his grandson the night a fierce rain came and unleashed havoc on this small city surrounded by rivers and mountains in southern Colombia.

From what the store owner has been able to gather, the torrents of mud, water and debris unleashed late Friday and early Saturday swept away his 18-month-old grandson, Jadir Estiven.

On Sunday, Vargas was searching for the boy and the infant's young mother — his daughter. The baby's father survived.

"They were hit by the strongest avalanche," said Vargas, who was so tired from the search effort that he could barely open his eyes or speak.

He is far from the only person in Mocoa searching desperately for young loved ones. At least 43 children were among the confirmed dead from the devastating flood, according to President Juan Manuel Santos. Santos later wrote on his Twitter account that he had been informed the death toll had increased to 254.

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The deluge smashed houses, tore trees out by the roots and washed cars and trucks away.

Search-and-rescue teams combed through the debris and helped people who had been clawing at huge mounds of mud by hand. Many had little of their former lives left to search through.

Rescuers search for survivors in Mocoa, Colombia, on Sunday. Fernando Vergara / AP

Gilma Diaz, a 42-year-old from another town who came to search for a cousin, said "people went to their houses and found nothing but the floor."

Santos, who visited Mocoa for a second straight day Sunday, declared the area a disaster zone. The president said the avalanche of water and debris also destroyed roads and bridges, knocked out power in half of the province of Putumayo, where Mocoa is located, and destroyed the area's fresh water network, creating dangerous and unsanitary conditions.

Mocoa is vulnerable to flooding. It is surrounded by the three rivers in a natural basin created by the surrounding mountains.

The danger has grown worse in recent years because of deforestation, which eliminates some protection from runoff, and because many people built their homes close to the water.

But the triggering event was rainfall of more than 5 inches that began late Friday.

"The rain fell on Mocoa with an intensity and force that was without precedent and devastating,"Santos said."It rained in two hours what falls in a month in Bogota."

A 1989 hydrology report for the Agricultural Ministry warned that just such a disaster could happen unless steps were taken to reinforce the riverbanks, channel water away from the town and restore some of the forest.

It was not immediately clear why those steps had not been taken.

Colombian officials pledged aid to rebuild homes, and the attorney general launched an investigation into whether local and national authorities responded adequately to the disaster.