Emergency crews searched for survivors early Tuesday after downpours triggered flash floods (searchthat tore through this town on the U.S. border, killing 31 and leaving at least a dozen more missing.

President Vicente Fox (searchdeclared a state of emergency in Piedras Negras, a town of 200,000 in Coahuila state, 150 miles southwest of San Antonio, Texas. Coahuila Gov. Enrique Martinez called the flooding some of the worst in the history of the U.S.-Mexico border region, saying "the magnitude of destruction is enormous."

Emergency crews had recovered the bodies of 31 victims, but said more than a dozen others had yet to be accounted for. About 100 homes were severely damaged or demolished completely and thousands of people were living in municipal buildings which authorities converted into makeshift shelters.

Fox ordered soldiers to the area to aid in search and rescue efforts as well as begin the process of cleaning the destruction of flood waters, which carried away cars, light poles and the walls and roofs of homes and left the area littered with furniture and debris.

Police urged those whose homes were still standing to remain in government shelters overnight, warning that a new wave of rain could trigger more flooding.

Five neighborhoods hit hardest by flood waters were without electricity, gas service and potable water, but Martinez said basic services should be restored to much of Piedras Negras (searchby Tuesday.

Some of the people whose houses were not completely washed away could be allowed to return home in the morning, if the rain holds off, the governor said.

The skies opened Sunday night, unleashing heavy rains and swelling water levels by 25 feet in the Escondido River (search), which flows into the Rio Grande. The downpours intensified and triggered the first flooding in a nearby town.

As the rain intensified, the Escondido poured over its banks, unleashing a wall of water that engulfed dozens of houses in Villa de Fuente, a working class neighborhood of tin-roof shacks.

At a shelter waiting for emergency rations on Monday, 19-year-old Maria Melendez said she rushed outside with her three children when she heard a growing roar in the distance. The family lived in a shack of sticks and aluminum in the Colonia Perodistas, another one of the areas were floodwaters first struck.

The three watched as water inundated some homes and toppling others. By the time they had returned to their house, the water was already seeping in from all directions. In a matter of minutes, their possessions had been washed away.

"Everything was turned upside down," Mendez said.

By midnight, the flooding had spread to several nearby enclaves, forcing dozens of residents to scramble on top of roofs or climb trees and light poles. There they waited for hours for emergency crews.

Flood waters receded by midday Monday, and Fox toured the area, promising to continue search and rescue efforts while also pledging to help survivors recover their homes and belongings.

"The army and all local authorities are going to find every person whose whereabouts are unknown," the president said.

A crowd of hundreds cheered the president as he spoke at a municipal gymnasium that had become a shelter where authorities distributed food, bottled water, blankets and mattresses.

Maria Concepcion Joaquin, a 32-year-old homemaker, was riding in a car with her husband, her sister and her sister's three children, ages 8, 7 and seven months when the floods struck.

They managed to abandon the car and the adults put the three children on the rooftop of a nearby house were a woman was already huddled. Seconds later the current swept them away, said Jaime Flores, Joaquin's 20-year-old nephew.

Joaquin's husband and her sister survived, but Flores' aunt wasn't so lucky. Family members discovered her body at a hospital where corpses were taken to be identified.

"Now they say they are not going to build houses in the river's flood plain," Flores said. "But why do they wait until a tragedy happens to say that?"