MOCOA, Colombia — Townspeople desperately searched their ruined homes and the local hospital for loved ones Sunday after a torrent of water, mud and debris swept through a city in southern Colombia, causing more than 200 deaths, many of them children, and leaving hundreds more missing and injured.

Neighborhoods were left strewn with rocks, wooden planks, tree limbs and brown muck after heavy rain caused the three rivers that surround Mocoa to rise up and surge through the city of 40,000 Friday night and early Saturday as people slept. The deluge smashed houses, tore out trees by the roots and washed away cars and trucks.

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

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

President Juan Manuel Santos, who visited Mocoa for a second straight day Sunday, declared the area a disaster zone and said the death toll stood at 210. But that was all but certain to rise because authorities said there were more than 200 injured, some in critical condition, and more than 200 others unaccounted for.

Dozens stood in the door of a hospital, hoping for news of family members who were not on the list of those confirmed dead or injured. Others frantically knocked on relatives’ doors, hoping to find someone with information about their loved ones.

Santos said more than 40 of the dead identified so far were under 18, perhaps because youngsters were already in bed when the floodwaters struck.

Maria Cordoba, a 52-year-old resident who was trying to wash her belongings in a river, said two of her nephews, ages 6 and 11, were killed when their house was destroyed. “The mother as well was totally beaten up” but managed to save her 18-month-old baby, she said.

A rescue worker in an orange jumpsuit emerged from one search area with the body of an infant wrapped in a towel. Not far away, Abelardo Solarte, a 48-year-old resident of Mocoa, held a child’s shoe as he helped clear debris.

“You have no idea how many kids there are around here,” Solarte said.

Jair Echarri, who came from a nearby town to help, also struggled to comprehend the loss of so many children. “I feel an enormous sadness because it’s filled with kids’ things, toys, clothes, school books,” he said. “I am a father, and this breaks my heart.”

Santos said the water and debris also 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 surrounded by 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.

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.

Juan Chanchi de Ruiz, 74, said the noise of the surging flood woke her up and gave her enough time to get to higher ground. Her house wasn’t damaged, but several neighbors’ homes were heavily damaged and many people fled with some of their belongings. “Around here, there’s nobody. Everybody left,” she said.

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.